Poloniex is the best exchange i know.
I used to trade on bittrex, but i've heard multiple reports that they are freezing accounts for "verification purposes" but never unfreezes even after verification.
This is an older topic but needs refreshing. Exchanges have recently really ramped up their demands in KYC terms. Its getting really annoying!
BITTREX is by far the worst, as they have locked up funds for existing accounts until you provide all the info they want.
The market demands exchanges which avoid KYC of this sort and I am certain people are willing to pay higher fees to avoid KYC forms.