For the me the best exchange platform is binance and bittrex it is the best recommended especially for newbies because there's a lot of features in these exchanges and eady to use you can also earn a big profit.
Binance has replaced the Bittrex in the last 2 years, but the Bittrex has been the most popular altcoin exchange for years. Especially during the 2017 bull market, Bittrex was unbeatable, AFAIK. Now the situation has changed in favor of the Binance exchange, so it is better to trade in Binance.