And which exchange has the lowest fees?
If you referring the exchange with lowest fee, check out Liquid Exchange from Quione, their withdrawal fees is Zero, yes it's completely without fees.
And Bittrex also one of good exchange and user-friendly, if you want to withdraw with low fees, try to withdraw with XLM / Stellar.
See if you look at the withdrawal then those exchanges are very good but you need to look potential about the exchange and their security measures. One more thing is some coins will not list in those exchanges, so before start trading thinks twice.