aside from needing the tank and heals obviously!! But i was thinking, what class/adv. class is the most useful? ops, or flashpoints? PvP? Rockin the house is your job... what is it?!

I have a merc that I just recently started doing ops with, and to be completely honest... i found it a bit boring. I've played (raided) in wow a Warlock for almost 6 years, also a hunter and a moonkin. My true question is how much trouble is a sniper going to have in boss fights when your going to need to move a lot... considering the cover mechanic, VS. the amount a sorc would bring to the fight. There are quite a lot of sorcs out there, and fewer snipers, which leans me more to the sniper aspect of it, but with the amount of movement i saw, it worries me having to pop in and out of cover constantly, loosing an extra GCD.