The best sites for me are:

Poloniex - They are one of the best trading site and they are doing their best to maintain their reputation and they always maintaining good amount of coins and only limited based on their activeness.

Bittrex - Most of the new legit coins are getting here which give you advantage to buy it on an early age.

Yobit - A lot of coins to choose from, if you know how the whales move then you are going to make a lot of profit.