Im using different exchange depends where altcoin I want to trade is available. Oftenly Im using bittrex, polo and hitbtc. Sometimes Im also using etherdelta to exchange erc20 etherium token specially if its just few tokens.
c-cex yobit polo bittrex is top of my choice right now there is a bounch of exchanger over there but the most reliable on me is this. they have 2fa which security is good but there are instances that it compromises that they can hack your account somehow we don't know what to do if that happens much better we don't share information or email address to others.
I do not really like c-cex first because their site very often do maintenance. Very often I fail to access c-cex because their site is very often down. I don't know the reason what makes the site very often down but it is really very disturbing trading activity. I prefer to use poloniex. There are many traders on there so make the volume on the market in poloniex very large then your order will quickly fill