Basicly. when all hell break lose you will have to be able to spam heal like crazy fr like 15 seconds.. after that.. you or the other team will be more or less gone. So yeah.. Pally = bubble and spam heal.. a bit slow heals thought but u can allways go flash.. as you dont really need the mana for a long fight anyway.. Resto shammy have chain heals, but.. they are 2,5 sec cast.. with heroisem a bit slower.. but first it seems like its best to just go crazy on the lesser healing waves.. and when a few targets are down continue geting all up with chain..
Holy prist, have aoe heals and stam buff which is nice but they might be a bit squisy... My fauvit so far is Resto drood... if he stay stealthed close to you.. the other team cant start focusing on him to get the healer down and that is a big + as most teams seem to go for the class / name that is diffrent from the rest.. SO.. if he stay stealthed he can just pop directly out in tranquility as it all breaks loos and heal each member of the team for 1600-2000 each 2 sec.. and then start stackin up hots on all hurted members.. You will have a NS+healing touch that can crit up to 10k.. Also, in some games where the other team have been really defencive as they know whats going on and staying behind pillers etc... we have some times had him root a target and i nuke the crap out of it in a way to get things going.. and they cant really do much about it... Just awoid using cyclons onless its really needed.. Like locking out a healer when you see the shammys are nuking on someone else.. but be carfull.. it easily fuck up some as i tend to change targets fast if i cant kill someone in a few nukes.

So if your intentions are to basicly help the shammys id say a resto drood is the best choice, as of stealth, tranquility and root