I also considered to choose between Bittrex and Binance. I finally choose Binance as it was much easier to start. Based on the fact that Bittrex has reached enormous traction the last months/weeks new users don't seem to be that welcome anymore.

The only negativ aspect of Binance: The interface is not very intuitive - so a lot of space for improvement

Positive aspect: Lot of altcoins are available, ICO LaunchHub for new coins gives the possibility to be an early bird sponsor on a quite convenient way