When looking at what char to run, you always need to consider what it is you are really trying to accomplish with the group (kills as much as fast as possible? Be able to do any/all progression? Survive just about any normal group combat situation?). If you are looking for the best overall DPS, then you should concentrate on melee or caster style. If your looking at versatility, then hybrid classes help a lot.
Your thinking on just swapping out shammy for better DPS, then I'd go Bst. Similar buffs/dbuffs. Great pet, melee and caster DPS (the new DoTs rock), heals, and can off tank/and pull.
A mage would give you a lot of boosts aswell. Pet off tank/ melee DPS, caster DPS, CoH for travel, pet kits, even a clicky you could pass to your Wizard (if you monitoring your group) for a weave/mana free casting item.
But it all comes down to what you want your group to do