After trying out YoBit,I'd want to start marginal trading.The usual bitcoins to alt and vica versa.The site must be very supportive,less document requirements and supports most of the altcoins.
Also I will be day trading at times or invest in a stable alt for a week/month.My main concern is support,they trading website must support most of the alts and definitely bots.
Poloniex is great for margin trading, but for day trading it's a little bit unusual because most of the trading bots and pumpers go straight to Poloniex, so for day trading sometimes other exchanges like Bittrex would be better.