I was debating between these three specs and I decided to calculate a few things and then to share it here.
The main differences between the three specs is that:
Deep Resto has Improved Rejuvenation, Improved Regrowth and Gift of Nature.
Moonglow has Moonglow and Nature's Grace. This spec may also have a couple points in Improved Rejuv and will likely have 5/5 in Gift of Nature.
Heart of the Wild will have Heart of the Wild.
All three specs are assumed to have Improved Healing Touch, Reflection, Tranquil Spirit and Nature's Swiftness. Since they all have those in common, I will mostly ignore those.

On research it looks like Gift of Nature and Improved Healing Touch type talents do not affect the spell coefficient, and are not affected the spell power. Luckily, this makes it easier to compare the relative effectiveness since it will not vary by gear.

Healing Touch(Rank 10) has 100% spell coefficient: 720 mana base, 648 for Deep Resto/Heart of the Wild, 589 or 583 depending on if Moonglow is multiplicitive or additive.
Healing Touch(Rank 4) has an 85.7% coefficient: 185 mana base, 166 for Deep Resto/Heart of the Wild, 152/150 for Moonglow.
Rejuvenation(Rank 10) has an 80% coefficient
Regrowth(Rank 9) is a bit complicated but the direct heal has a 32.5% and the HoT has a 51.3% coefficient.

Gift of Nature is worth 208 +healing in regards to Healing Touch Rank 10 but only 48 for Rank 4. 94.5 for Rejuvenation and 253 for Regrowth. Improved Rejuvenation is worth 142 +healing. The value of Improved Regrowth is a little harder to nail down, but since only the initial heal can crit I would say it only increases the average effectiveness of Regrowth by 25%. However this is magnified a bit with Nature's Grace.
Its a little hard to pin down what proportion of spells we will be using but unless someone has a better idea, I am going to assume about 60:40 Rank 4 vs Rank 10 for Healing Touch and assuming that Rejuvenation will be be sniped by other healers and Regrowth is just a bit too expensive and the HoT will be sniped as well. There is a case for Moonglow using Regrowth primarily due to Nature's Grace.
Mana efficiency: Moonglow will save 9% mana over the other two specs, and Heart of the Wild will have more mana. To compare the two, we need a baseline for total mana. Using sixtyupgrades, it looks like Night Elf Druids have 100 base Int(2744 mana) at 60 and Tauren have base 95 Int(2669 mana). Throwing in some pre-raid BIS gear... using the same website and... the default resto filter doesn't value Int very much, gaining only 64 int on gear. This gear spec also has like 2.6% chance to crit with spells. However, it does have 427 +healing. Which feels kind of weird having a mana pool of only 3629. Heart of the Wild would add about 465 mana.
Throwing on T1 gear and +healing plummets through the floor to +200ish but it has 327 from gear with 6074 mana. And nearly 9.5% crit chance. Heart of the Wild would add about 966 mana and another 1% crit from Int. Who knew T1 would be a 'down-grade' of 200 +healing?
Of course, Heart of the Wild would be affected by buffs so that is something to take in consideration as well.
I think there are just too many variables to calculate (buffs/rotation/regen/etc) to work out which spec is best in all circumstances, but it seems to me that pre-raid BIS gear gives the advantage to Moonglow, Dungeons/small raids gives the advantage to Deep Resto (because less/no heal sniping), and the T1 set is itemized more toward Heart of the Wild because of all the Int on the gear.

Everybody knows that debuffs in classic are precious, so I thought I'd put together a list and open it up for discussion whether I've missed something or which debuff is more valuable or if a particular class/spec is better at applying the debuff.
Debuffs use a priority system, where lower priority debuffs will be dropped if the debuff cap is reached. For Classic the debuff cap is 16 debuffs. CC/Taunt effects have the highest priority. Curses/Sunder/Thunderclap type abilities have the second priority. Vulnerability type debuffs(like winter's chill, shadowweaving) have third and DoTs have the lowest priority.

Armor reduction debuffs:
Curse of Recklessness: Warlock #3, depending on how the final armor values shake out, we may only need this curse on Warrior type bosses
Sunder Armor: Protection Warrior #1, Pro-tip: every Warrior hits Sunder Armor once at the start of the fight to stack up to 5 instantly.
Expose Armor: Rogue, however does not stack with Sunder Armor. If talented, a 5 point Expose will reduce armor by 300 more than a full stack of Sunder Armor.
Annihilator: Warrior(s) Pro-tip: multiple dps/off-tanks with Annihilator to stack up, then swap to their regular weapons except for 1 to keep up the debuff. Lasts 45 seconds.
Faerie Fire: Druid, easiest applied by a feral druid off-tank using Feral Faerie Fire.

Magic damage increasing debuffs:
Curse of Shadow: Warlock #1
Curse of Elements: Warlock #2
Winter's Chill: Frost Mage
Shadow Weaving: Shadow Priest, however a Powerweaving(heavy Disc but enough for shadowweaving) or Holyweaving(heavy Holy, but enough for shadowweaving) Priest can fill the role as well. Typically Shadowweaving will take up additional debuffs slots from Shadow Word: Pain and Mind Flay, although once it is stacked up to 5 it can be easily kept up with Mind Blast on cooldown, say from Power/Holy weaving spec.
Nightfall: Phase 3, Off-tank Warrior is considered the best wielder of Nightfall because that gives them something to do when not tanking. Enhance Shaman/Ret Paladin/Wing Clip Hunter may have better uptime but these specs tend to be low priority for gearing.
Improved Shadow Bolt: Warlock, preferably several to keep the debuff rolling.
Improved Scorch: Mage, though we shouldn't see this until later phases as most of the bosses in MC are very resistant to fire damage.
Flame Buffet: Arcanite Dragonling, though we shouldn't see this until later phases as most of the bosses in MC are very resistant to fire damage.
Judgement of the Crusader: Paladin increases holy damage. However, unless you have a large number of Smite Priests it is not worth the debuff slot.

Ranged Attack Power
Hunter's Mark: Hunter, can be talented to increase the attack power. Since this debuff really only affects Hunters, unless you have quite a few in the raid it should probably be skipped.
Expose Weakness: Hunter from the 8 piece bonus of T2. It doesn't last very long and only affects Hunters.

Physical Damage
Hemorrhage: Subtlety Rogue, however does not stack with Gift of Arthas and has limited charges. Replace that rogue with a gift from our lord and savior, Arthas. I may have mained a Death Knight...
Gift of Arthas: Main Tank, this is effectively adding a Dense Sharpening Stone to everyone in the raid. Assuming that a hunter with a 3.0 weapon uses a pet with a 1.5 attack speed, this is better than Hunter's Mark even for the hunter. Hunter pets, Rogues and Feral Druids get the most benefit out of this debuff due to attack speed.

Mitigation
Thunderclap: Warrior, since this is only usable in Battle Stance, either an off-tank or an Arms warrior should keep this active. The main tank can do it in a pinch, but it requires stance-dancing.
Thunderfury: Warrior, this does not stack with Thunderclap, but is better anyway.
Demoralizing Shout/Demoralizing Roar: Warrior, because Demoralizing Shout is a larger reduction in attack power, though both can be talented to increase the amount.
Curse of Weakness: Warlock... #4?, reduces the damage of the boss by 31, though can be talented for an additional 20% and further amplified by 50% from Amplify Curse. Reducing a boss' damage by 55 damage may not sound like much, but that is roughly the equivalent to 780 attack power. However, very likely to be skipped.
Insect Swarm: Druid, while it does reduce the chance of the boss hitting by 2% it is likely not worth the debuff slot.

Notable Miscellaneous
Ignite: Mage, though we shouldn't see this until later phases as most of the bosses in MC are very resistant to fire damage. Ignite may buck the trend and actually be on the Vulnerabilities priority.
Judgement of Light: Paladin, melee attacks against the target heal for a small amount.
Judgement of Wisdom: Paladin, attacks and spells against the target have a chance to return 59 mana.
Vindication/Scorpid Sting: Ret Paladin/Hunter, it is unclear how raid bosses are affected by Strength/Agility losses.
Vampiric Embrace: Shadow Priest, however to get the most of the healing you would need to allocate 4 debuffs to that shadow priest alone.

So what am I missing other than explicitly listing out the best 16 debuffs?

Is Slam/Imp Slam really so terrible as 2h Fury? Sure it resets your swing timer, but we've got swing timer addons to time that correctly now. And its half the rage of Mortal Strike but still does similar damage. It is still weapon damage plus some static, where the only drawback is that the static damage is about half of MS. But its also half the rage.
Pretty sure Slam triggers Flurry if it crits but does it use up a charge? Flurry makes up for the DPS loss for the cast bar of Slam compared to using instants like MS/Bloodthirst, so it looks pretty good on napkin math. Like, if Arms is assumed to have the rage to MS on cooldown, then Fury could Slam after every auto-attack. If Slam does trigger Flurry, you would need a lot less crit to keep it active since you are nearly doubling your opportunities to get a crit.

Why stop with Hunter's Insignia Medal as BIS then? Just because its a quest reward? The BoE green necklace, Prismatic Pendant, is 16 stam over the Hunter's 15.

Some drops/quests for 20-40:
Staves
Rod of the Sleepwalker from BFD(req 24: 2.8 speed, 23.75 dps, 11 int/10 spirit)
Wind Spirit Staff from RFK(req 27: 3.3 speed, 26.67 dps, 5int/3 stam/15 spirit)
Loksey's Training Stick from SM Library(req 31, 3.1 speed 31.29 dps, 60 AP vs beasts) - likely low drop chance (8%)
Illusionary Rod from SM Library(req 34, 3.4 speed, 34.71 dps, 15 int/7 stam/10 spirit)
Spellshifter Rod from ZF quest(req 40, 2.7 speed, 35/74 dps, 16 int/6 stam)
2h Axes
Skullsplitter from Call to Arms elite quest (req 30, 2,9 speed, 30.17 dps, 15 str/4 stam)
Bonebiter from SM quest (req 34, 3.4 speed, 38.82 dps, 20 str/10 stam)
Tok'kar's Murlock Chopper from Swamp of Sorrows quest (req 35, 3.2 speed, 32.50 dps, 15 str/6 stam)
Corpsemaker from RFK (req 29, 3.8 speed, 28.95 dps, 15 str/8 stam)
Thermaplugg's Left Arm from Gnomergan (req 32, 2.7 speed, 32.59 dps, 18 str/7 stam)
Ravager from SM Armory (req 37, 3.5 speed, 37.29 dps, whirlwind proc)
2h Maces
Manual Crowd Pummeler from Gnomergan (req 29, 2.0 speed, 29.00 dps, 16 str/5 agi/3 charge use for 50% attack speed)
Mograine's Might from SM Cath (req 39, 2.8 speed, 38.92 dps, 17 stam/16 spirit)

Basically, get the Staff from BFD, then Corpsemaker from RFK, then do the SM quest as soon as you can. So you don't really need the 2h Axes/Maces talent until 29ish.

edit: updated with item links because I figured out how to do so, lol

Comments on Egan's talks about how you keep it after turning in the quest, someone will have to double check when Classic launches.

There are a couple idols in phase 5, the claw/rake one, the rejuv one and the cast-time healing touch one. Nothing for tanking.

The idol looks to be phase 6.
Malefic and Ash boots do look to be phase 2.
I would recommend mentioning Totem of Infliction, even if it is Alliance only for offhands. Combined with the Rubidium Hammer it gets you most of the way to a Warden Staff at 170 armor.
The Gargoyle Slashers gloves should probably deserve a mention as well. Str/Agil/Stam/Crit gloves out of Scholo.
Otherwise, looks great!

Has anyone double checked the Orc Stun Resist Racial on Classic yet?

I remember some discussion about whether it increased stun resistance by a flat percent or multiplicative with the base resistance.

IE: 15% base (unsure actual %) +25% = 40% or 15% * 1.25% = 18.75% resistance.

Should be fairly quick to check, but I don't have Classic access.