Gaudion wrote:
Priests are more in demand than Shaman are nowadays thanks to a couple Naxx encounters that require them. They're more dynamic healers, capable of both strong raid healing and strong tank healing as well as being (in my humble opinion) tied with Druids for the strongest five-man healer since they're so well-rounded.
Shaman are more specialized healers. They're capable of single-target healing but are very poor at it when compared to the other three healers in the game. They're exceptional raid healers, though unless there is a constant output of high AoE damage (on fights such as Sapphiron) they're honestly not any better than Holy Priests or Resto Druids. To their credit, they do still bring several nice buffs, and although some can be brought by other classes, a few can not.
While I fully agree wtih what Gaudion had said, on our server, priests are 'meh' on the "In demand" category. So many people are making priests they're not really needed anymore (per se).
And quite honestly, as a shammy healer, the only type of healer I cannot ever get above on the healing charts are druids. I may get lucky on the occassion crappy one, but other than that, I'm usually second on the charts. For some reason, every priest healer I've run with seem to lack in heals when it comes down to bosses, and I mean lacking big time.
As I said, it could just be our server, as every one is different.
Now don't get me wrong, because what Gaudion said is quite correct, just speaking of my experience with each type of healer. I've got a priest right now at 48 and am loving it (though I'm shadow).
A suggestion is that you can play your shammy while with your friends and if they're not on, you can play your priest. This way, you can get a feel for each one and in the end decide which you like better.
Some people like healing on shammies, others like healing on priests. It's all a matter of opinion. An example is the fact that I completely hate healing on my pally, but I love it on my shaman.
Good luck!
(and very nice response Gaud).