I use both exchanges, they are both excellent. I will note the main differences of these exchanges:
1) There is no margin trading on the Binance, but there is on bitfinex. Margin trading attracts market participants, especially those who trade deposits of 30 000 - 500 000 dollars.
2) I like the opportunity to participate in the ICO in the Binance and invest in BNB tokens. This is cool, because many good projects can not go on long for good exchanges.
3) The best thing about bitfinex for me is the ability to trade a large number of assets to USDT.