You really should just play the class you think you would enjoy the most.
What class will be the best dps is very hard to tell. When ch 4 comes out mages and scouts are being balanced. Scouts might stay or mages might pass them BUT after every patch 2 more classes will be balanced giving a chance for a new class to be the top Dps.
The best true way to find out is to wait till all classes are balanced. You never know if RW changes who should be number one. It could be warrior or rouge. Maybe even warden.
So best thing is play something you enjoy, stop thinking about being number 1 and better then everyone.
On a side note, i think warrior should be the Number one over dps due to the risk factor they have =)
scouts have very low risk when in partys, mages have some risk but not close to warriors and etc.