Warrior, don't go prot until you're either 70, or very close to it. The time it'd take to level during instances only, makes switching to protection spec not worth it right there. But, once you're 70, yeah, find a good raiding guild and you'll always be running Karazhan and Gruul, and so on. You will probably also be first in line to get the tier gear drops, if it's a warrior item, and you are in fact a good tank.