Well the best hitters in Mid for melee in rvr are no doubt berserkers and savages. For casters I would say Runemasters. Spirit Masters are really good for more of small group action and warlocks hit amazingly hard but are kind of dead in the water after chambers are down so most people don't look for them to add in groups.
As for your shaman spec, are you on the classic server or on a TOA server? If you are on classic you'll be loved with high AUG. Cave shamans are nice and fun and all, but if your looking for a serious group action having higher aug again for buffs/shears/resists, will again be better looked upon.
I am not a shaman expert so I will point you to a better place to ask about how to spec your shaman.
http://vnboards.ign.com/midgard_seer_professions/b20913/p1
There you go, anything and everything you'll ever want to know about shaman will be in the those boards.