Binance, Kucoin, and Coinbase.

why Binance? I think it should be pretty obvious that Binance has the largest volume for altcoin market. I also like Kucoin and Binance because their interface is amazing, especially KuCoin. Binance also has a lot of development going on. They are currently developing a decentralized market, the one that we crypto enthusiast have been dreaming on. What's more important is that they both are secure, never had any hacking or problem with them.

I also would like to see my favourite coin getting listed in Coinbase because it's the current generation of Mintpal. Every coin that gets listed there is getting pumped, LOL.