I define a good exchange in two ways...

According to Design of the Exchange:

I have heard an experience that I wanted to use an exchange that was recommended to be because it was very secured, when I logged into the exchange, I couldn't navigate the exchange to convert or trade coins. I was obviously lost, it is not because I am new to using  exchanges because I have been using them for long.
It is because the design of the site was not User Friendly. I love it simple and unique and not to be obsessed by too many colours. With that I am comfortable with the design.

Secondly, the reputation of the exchange. I cannot have coins in an exchange and be finding it difficult to sleep because the coin is not safe or because I pressume that the coin is not safe. When an exchange is very secure, it will have good reputation in the future. That is why is stick to binance.