I use bittrex.com, I think it's the best, accepts almost all the cryptocurrencies that are quoted in the market, it offers you 3 options when it comes to buying or selling your cryptocurrencies, depending on which so fast you want the operation and the change.

It is very safe, it registers you and asks you to authenticate your account, either with your identity card of your country or with your passport.

The commissions are very low, especially if the amount to change is high, it is practically four times less in order of magnitude to the changed rate.

Your environment is very friendly, and very intuitive at the time of performing operations, in each operation has a time to camcelarla, the utimo step to perform the operation is a verification mail that comes to your mail.

So far it is the best I have tasted.

regards..