Just to throw my vote into an informal poll
I use Bittrex for 90% of my stuff. Easy and seems to have a good reputation.
Bitfinix, just because it was the first exchange I found and had a coin that wasn't on bittrex.
etherdelta.com. Just started using this. seems good, a little slow with transfers if the eth network is busy and the interface is a little more confusing. But once you learn it, seems like a good place to easily trade ecr20 stuff.
No personal experience with the below, but seem to be popular around here.
poloniex
kraken
binance