Check out the skill calculator in the summary. There's a lot of different possibilities (Unless I screwed my math up, something like 170,000,000 combinations of skills/runes JUST for the barbarian class. The other classes look about the same give or take a few million combos). Obviously some combinations will be better than others, and even the "best" build will be pretty situational for a given class depending on what you're doing and your playstyle. Personally, I like how they're allowing some more flexibility with abilities by getting rid of skill trees and allowing you to change what skills you have relatively painlessly. When I played Diablo II, I spent a bunch of time leveling a druid, only to realize after I'd played for dozens of hours that my I had allocated my skill points stupidly, and there wasn't anything I could do about it other than make a new character or deal with it.