Bittrex, EtherDelta and Binance because of big number of coins/tokens
When it comes to tokens and being a decentralized exchange, I will definitely give it to Etherdelta. Moreover, since it is all token to Ethereum trading, one will just have to adapt.
It is a very comfortable site to trade and things have been pretty cool lately since all the laggy issues have been fixed which was more like pain in the ass for a while. Asides that, it is bittrex anytime any day. I have not really tried others though, but I know there are some exchanges I cannot definitely try.