Healer demand > *
Be a holy paladin if you want to be able to heal one target very well (and you get to wear plate, you can even sometimes tank for 5-man but your potential damage output outside of raids is the worst)
Be a resto shaman if you want to be able to heal groups very well (mail armor, which is nice, and you can do lots of damage when you want to)
Be a resto druid if you want heal over time spells, which is great for individuals and groups (leather armor, lots of damage or tanking when you want it, go go magic healing tree)
Be a holy priest if you want a mix of all 3 (cloth armor, great damage output outside of raids)
The advantage of being able to wear higher tiers of armor is that you can swap out for lower tiers whenever you want. For instance, paladins can wear any type of armored healing item but priests can only wear cloth. However, I'd argue that paladins get the short end of the stick since they can barely do any damage and are in general in lower demand due to their specialty of healing the tank really well but groups not so much.
If you don't want to be a healer, make any ranged DPS class that isn't a hunter.