Good exchange is exchange that operated more than 2 or 3 years and they has good reputation, never get any hack and comply with the regulation in the country their located. I used Bittrex and Poloniex more than 2 years and i have balance in that exchange also since 2 years and untill now that my balance is safe. So this both exchanges is one of the best exchanges.
Necessarily does not have to be more than 2 or 3 years, but most of the time, there is always something that comes with reputation and for an old exchange that has been doing well, it is normal for traders and investors to want to tend to that area.
Moreover, if we are to be looking at years, I am sure HitBTC has been on for quite some years now, and if we really are to judge based on that, I am sure you will definitely know the answer to give in terms of using HitBTC or the likes of Yobit.
There are new exchanges that are building good reputations, have a nice platform, very good fee and a nice support, and as far as I am concerned, as long as you know the exchange is compliant to a regulatory body and all these things are in place, then there is nothing stopping you as a trader from using such e.g. the likes of binance and Kucoin.