Definitely Binance right now, their support is probably above average right now, and there's a lot of people using them and jumping ship from other exchanges due to the fact that they are one of the better exchanges out there. As magneto said, it's just a nice balance for sure.
Binance's BTC and altcoin withdrawal fees consistently rank among the cheapest available, as well.
You can't really say that an exchange is best just because a certain crypto's withdrawal fees are the best available though, because not only do withdrawal fees differ within an exchange depending on the crypto you are withdrawing, you're not considering the security of your funds at all.
Check out this thread: https://bitcointalksearch.org/topic/exchange-withdrawal-fee-comparison-3690816, it's got a nice table.