For me it is Yobit of coarse !! There can be no other !! It's even in my signature ^^
Well besides them I do like coinexchange and novaexchange.
I think alcurex has potential but right now they simply do not have enough coins. There are many coins I have no idea why they do not have. I have used bittrex and it was just fine no problems at all. I use them as secondary if I find a better price there. I have tried bittler too. ( I think thats the name) I can't remmeber so I guess they were't that great.