Last time I played during S2, they were still mostly shit tier and only used for high GR farming as tank/pull/support and shit but they were terrible to play, they had some new sets and shit but all of them were fairly weak cause they nerfed them during the PTR. They could like, kill a boss really fast, but couldn't clear trash for shit. They get some new sets for S4 so they might be good I don't really know as I haven't been following enough. With the cube changes and stuff though I think you'd be able to make most classes pretty fun to play by cubing the legendary effects that eliminate the weakness of your specific build better.
I'm not sure what I'll play, I think I don't want to play a DH this time around, maybe WD or Wizard. Or maybe Monk. We'll see when it gets closer, not sure I'll even play this, depends on what I'm doing when it starts. If it started NOW, since I'm not playing anything, it'd be a different story but 3weeks from now, who knows. Installing PoE atm, I'll probably play that for 2-3weeks then I'll see.