Base from the story of successful altcoin traders they recommend bittrex, high performing altcoins are listed on that platform and I think thats the best exchange for you. Their platform is also friendly user. But if you want super cheap altcoins you may try yobit but be careful because there is a lot of altcoins there to be delisted from the platform but sometimes there was a luck in altcoins with 1sat price because they pump up to 6x or 6sats so once you got lucky you will gain enough profit.😁