All heals are fun! It all depends on your style of play. You can even do well with a Holy Paladin if you like them. They have great defense, dispel poisons, bubbles, 6sec stuns, can glyph into a 5% raid buff, very speedy...
MW if played right are a constant instant cast healer. Although, you have to watch your mana and stay with a group. MW are easily interrupted as well. And you have to switch stances if you want to mount any kind of attack.
Shamans are the kings/queens survivability right now if they are geared/enchanted/talented correctly. Even racials can play a role on survival for a healer. Rocket jumps have saved my bacon untold amounts of time on my level 20 along with Nature's Guardian/BM trinket. They can decurse/dispel, interupt, slow, DoT and can offensively dispel! They have pretty decent damage too 1v1 because of their speed they can run circles around most classes, literally. Shamans have LOTs to do in a BG. Good shamans should be
#1 on the dispel list along with a HPaladin.
Disc Priest are very vulnerable 1/2 of the time. The other have of the time they should have a shield on themselves. Unless an opposing shaman dispels it. Priest can be fun if you like to do a little damage as well. Priest are normally at the top of the healing chart since absorbs count as heals now. And most, not all, disc priests just go willy-nilly with the shields regardless if you need one or not. Which leaves you vulnerable when you really need one.
/cheers