I started trading on Poloniex few months ago and when it temporarily stopped trading steem. I found Poloniex overall very easy to use and loved their charts(still use them).
Since that incident I opened an account on Bittrex and started using that. I found it had too many fees compared to Poloniex and I hated their charts. I also didnt like that I had to confirm any transaction to withdraw, made it bothersome.
I sometimes use etherdelta now and love it because you have one address for depositing all tokens unlike the other 2 which have specific ones for each one and if you for example send bitcoin to an ethereum address your coin is gone. One thing i dont like about it is you dont really have a proper graph but more like a boxplot that shows minimum and max for the day and last traded price.
What about you which exchange do you like to use and why?