For Altcoins, I'd prefer Poloniex at the time being, but if i ever need to exchange Bitcoin. I'd use Bit-x, why?
Poloniex:
Fast and easy, simple UI etc.
Bit-X:
Has "mining" implemented, you can sell your BTC and withdraw fiat, new Bit-X Debit Card is on the way which will probably keep you away from touching cash again.
So yeah, at the time being. Altcoins = Poloniex, Cloud Mining + Bitcoin = Bit-x.
To withdraw for cash bit2me is much better than bit-x. Check yourself.
And that de bit card that bit-x provide takes a big fee.