I like Bittrex and Poloniex because I started off there, but lately they have not been the best in the world. Hard to argue with Binance not being #1 and I also like Kucoin quite a bit. Cryptopia wasn't bad last year, but they really have not had their stuff together this year.
I also started with Poloniex, and I say the same thing that their rating has gone down. I like the Binance and Kucoin.