I think one of the best is kucoin and binance. I preffer kucoin.
Like most people on here, there are many platforms people use but once you get through these comments you should see that Binance is among the top platforms and that's not just coincidence. This is the fastest growing exchange at the moment, and one that many people trust and use. Depending on your needs though there are other ones also, one that I've used due to its volume is bestchange. In anyway, still be cautious when choosing the one for you.