I'm in love with Bitfinex. It was my first exchange since the beginning, and I've been trading on it for 3 years already. Tried other exchanges, but they never satisfied me as much as my Bitfinex did. I even had a terrible experience with some other exchanges but will tell about it in other reviews. As for Bitfinex, it's secure, user-friendly and, the most important, it cares about you. Support usually responds in a few days (it's ok for such a large exchange). There're some interesting features for prof as margin trading, funding (can hardly be found on other exchange), OTC and some others. Finally, they suggest unlimited withdraw.