For leveling purposes, go with a 2h Staff. It will provide you better magical damage because there aren't any offhand weapons you can use in the 55 and lower range. Shield is predominantly for PvP. 2h Staff is very easy to use and very cost effective. If you get deep into the endgame and want to really upgrade, I suggest you get the Wand + Hammer combo. It for sure provides more magical damage and healing power than using an Annelia's Left Hand (Healing Shield). While you do lose a lot of physical defense, you gain much more from using an offhand hammer and shouldn't be taking hits in instances
at all really. A lot of other priests don't even have to opportunity to see the true advantages of using an offhand weapon.
Comparison for those of you skeptics out there:
runes database comparison
Yes for leveling absolutely go with a staff. There isn't even a good wand until RT level imo. After that what weapon combo you use is purely based on your play style.
So from this comparison, you would get like 550 healing added from the extra mdam. It really isn't that noticeable if you are already endgame statted. 10k pdef base is extremely noticeable. And in GCH and Tosh hard, even in sc I can't tell you how many times the tank has been stunned or just did a crappy pull and I end up tanking. The shield has saved the party and myself a dozen times at least.In "deep endgame" I usually am the tank and I am two or three manning boss fights. So saying you
shouldn't be getting hit in instances is not all that realistic. Considering my GH when buffed can heal for twice of most peoples hp, I am not sure what the benefit would be besides having the mdam for killing mobs(which you wouldn't be doing in instances).
Like i said, you can use whatever you want based on your play style. But in answer to some of the questions in this forum, yes priest combos use a shield - in fact I don't think I know any endgame priests that don't at least have one.