Shadow is great for leveling up and soloing although as a priest you don't have to solo much if you don't want. Also, unless you're in an organized PvP guild, shadow line will let you have the most fun in PvP.
For leveling? Just do quests. All you have to say is Priest LFG in general chat and you'll be in a group in a few minutes.
IGN has a pretty good talent calc and some resonable premade ones on there also.
http://wowvault.ign.com/View.php?view=Talents.View&category_select_id=6
Edited, Nov 29th 2006 2:16am by MookusOU