I wanna suggest you to Coinbase but there are few coin you can buy or trade. Binance, Okex and BIBOX I trust, if my list more increase then Bitmex, Bittrex, bithumb etc. Binance and Bittrex has more than 250 and 265 trading pair where you can buy and also trusted. Okex has more 400 pair. But you shouldn't follow top CMC lists because there has some fake volume exchange list like P2PB2B exchange.