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.