@Chain1 If you are on tank duty, then full T1 is good. But that is only the case if there are other tanks or perhaps dps close enough (10 yards I think), and they also have to be taking damage (trash, maybe Rag and bwl-dragons etc). Otherwise maxed +healing (and +mp5) is better in pure tank and spank fights (razorgore, vael etc).
If you on the other hand are on both tank duty and raid healing, perhaps at the same time, then the choice between T1, 3 set T2 and +healing becomes more interesting as it could depend on the fight, what off-pieces you have and also your raid composition and tactic.
If you are on purely tank duty, and that tank is all alone at a certain spot, the reason full T1 isn't great is because the 5set would only give you about 7-15 mp5, depending on what healing rank used and that mp5 calculation is only true if you never cancel a heal; and 8set bonus wouldnt do anything at all.
Therefor I would say it is good if you pass T1 to the tank healer for those specific fights mentioned, but it is also good to have all shammys have T1 for certain raid healing and the fights I mentioned above with f.e. multiple tanks close to each other.
On a sidenote, but perhaps given, full T1 obviously scales worse, since you cannot upgrade your items. So the more offpieces you pick up with big +healing, the less viable full T1 perhaps becomes.
I could however be misinformed.