Binance for these reasons;
1- Bittrex won't let me sign up and that's been that way for a very long time.
    So what is their problem? No support ?
    Binance slowed down sign-ups but they still manage to do them.
2- Binance fees are cheaper.
3- Binance website is faster, page loads up instantly, Bittrex takes several seconds.
4- Binance interface is smarter/easier with both newbie and advanced features.

And I think they are now based in Hong Kong so mainland China regs. do not apply.
The only reserve I have about Binance is they are using Tether, which seems to be
a huge problem in 2018 with Bitfinex tampering with the market.
In the end after Tether & Bitfinex implode I think Binance and the Crypto market in general
will survive quite nicely. Just don't get caught holding USDT, which is simple enough to do.