I've used more than seven stock markets by now. The longest I used was Poloniex. I'm happy with most of them, but I don't like Yobit and a few exchanges. I don't know why my favorite poloniex. Poloniex is the first stock market i used maybe this is the reason of that. For me, Poloniex seems safe. The processing speed is also fine. I haven't had a problem until now.  if someone wants to get an idea I suggest Poloniex.