I've been on Bittrex for quite some time and it's been my primary trading platform. It's good to see others moving to it now. I just hope they have planned ahead so that their infrastructure is ready for all the influx of new users!
The only issue I've ever had was some coins lacked enough volume. With all the new users moving to the platform, that should help. Apart from higher volume, the only other thing that I've liked better on Polo is the price charting but Bittrex's isn't too bad.