Ok I have a lv20 Troll Shaman and basicly they are classified as Healers right.. for raids and such?

I was wondering what Melee weapon I should use, if any?
Is it good for a Shaman to be using melee at all, and if so is it best to use a 2h weapon/stave OR like a mace with shield for higher defence ?

At lv20 what is the absolute best weapon I could be using?
Out of them all, 2handed, Mace+Shield, 2h maces .. anything

The Stave I have right now is called

Medicine Staff of The World
+4 Agility
+4 Spirit

25-38Damage.

What is the best Stave I can be using right now at my current level of 20 ?