There are so many platforms or exchanges but i prefer to use bittrex and binance because they have a faster transactions than other platforms.
Yup now we have many trading platforms but in that highly rated sites are Bittrex, poloniex and Binance. You can use any of these websites. I will recommend Bittrex because I will use this site to do my trading activity and till today I did not face any issues in this site. This is my personal experience, you also can others suggestions and choose your best.