If you are new to crypto trading, and looking for a platform to trade, here are some platforms I use.
Share with all of you

1.
Binance (Strongly recommended)
2.
Bitfinex (Stable, not many coins available)
3.
Bithumb (
ps:security issue happened, consider well)
4.
Upbit (Korea exchanges)
Welcome to other suggestion

*******Additional information************
Recommended by FlamingFingers :
Bittrex - 2 years exp. and No issue ever
The four platforms are good enough but I will add another one which is OKEx launched by large Chinese bitcoin company, this application maintains strong liquidity in the CNY / BTC pair and manages two main entities including a focus on China's main domestic and international markets, due to exchange it is one of the largest crypto exchanges in the world