Both IDEX and Forkdelta are decentralized exchanges which might reduce transaction fees but add much pressure and stress upon selling. These exchanges also can't provide security of your tokens, hence increasing risk factor. On the other hand Binance, Bittrex have slightly have lower fess in comparison to exchanges like HitBtc, Kucoin and so on. I personally prefer Binance because it makes selling and trading of tokens in an easy way and user friendly environment on both website and on mobile app.