I have a mixed caster group, leveled them right at the launch of WOTLK and my idea was to have the most buffs/debuffs for casters.

Ranged classes typically have an easier time dpsing as they don't have to worry about melee range or attacking from behind a mob for parry/block etc.

My priest healer is in the tier 9 badge gear and easily heals everything so far (up to 10 man TOC regular) but it is more about what you would get enjoyment from.

I tried hunters and got them to 65ish but they didn't seem as much fun to me, too many "proc based" abilities instead of just dps macro spam and nuke stuff.

Everyone's opinion is going to differ but the reason a lot of people play shammies (I played them through Burning Crusade) is that they have great synergy and they can all heal in a pinch, they do great dps and having multiples of them means you have more buffs available.