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.