There are many really good exchanges out there which can be trusted like Bittrex, Poloniex, Binance,etc., I mostly use Binance now(I used Bittrex and Poloniex before). Sometimes, I also use Kucoin for the cryptos which aren't there on Binance. As far as decentralised exchanges go I prefer to use Forkdelta and IDEX(Etherdelta was my first choice but I left using it because of the hack and all) and for NEP-5 tokens I use Switcheo.