NO 1 poloniex, NO2 bittrex.

Most of altcoins list on poloniex are good and legit coins, XMR, STR, MAID are all good coins, and with highest trading volume.

While bittrex likes add new alts very much, and most of them are shit and scam coins, especially last year, bittrex always listed scam coins, and when the scam coins listed there, the devs dump them to investors. And then vanished, there was also some scam coin ICO were held there, very disappointed about bittrex.