The largest bitcoin exchanges by trading volume, Bitfinex offers plenty of advanced trading features. Fees are relatively low, as compared to many exchanges.
Note that Bitfinex is currently at the heart of allegations of market manipulation using potentially uncovered USDT tokens:
This means that Tether / Bitfinex is at risk of a) running on fractional reserves like Gox in the olden days or b) getting nabbed by the SEC like btc-e. Possibly both.