In seriousness, I think PER is the best overall stat we have. But as has been stated, a guy with a 16 can be worse for your team than a guy with a 13, so you don't just assemble the highest PER's and tell the league where to mail the trophy.
The trend in statistics is towards efficiency metrics which I think gets overrated. I think a player's efficiency is important, be it PPS or TS% or the much revered Locke Offensive Rating. But outside the superstars, who mix efficiency with volume usage, you want a mix of Efficiency Heroes with less efficient guys who have unique talents. Plenty of inefficient guys in the league I would take over the efficient ones.