It is a minefield in my current experience. It also depends on where you are based.
If you google for reviews on the sites listed above that will give you a lot of the information you need... Bittrex I have heard more positive things about , Poloniex is a scam site now. Livecoin sounds dubious...As are many many others. I am trying to buy some newer currencies but I cannot find even one place that I can use that I would trust not to steal my money. It is a joke. Some excellent prospects out there but this underindustry is so full of scammers its not even funny.
I have quite a lot of experience trading forex and futures, I thought that was a dodgy industry this one makes it look 100% legit!!!
Hopefully others will have some recommendations... I am still looking for dogecoin, antshares