For me poloniex still better because they have margin trading, i am good at predict up/down trend so i love poloniex.
I do not know how long is going to take, but I noticed bittrex will soon be introducing Margin trading and that should also give them an edge. How soon is something we do not know but may be pretty soon. Asides that, I feel bittrex is still better when it comes to the user interface and some tools that can make traders to do analysis easily which was the main reason I switched to bittrex anyway.
Support was good but now it is getting shitty which is expected considering the fact that they are being bombarded by mails when they decided to lock out people's account without notifying them.
poloniex is now one of the great and excellent exchangers. but bittrex in the future will be a great exchanger with pernyempurnaan system would be better. we just wait for bittrex to be a good exchanger.