A good exchange must have easy to use trading platform, a trusted name name and good chart for tech analysis will surely attract me trade with them.
Low liquidity is surely a no no for me, good liquidity gives opportunity to cut your position at competitive rate.
How a platform will be easy to use ? Because I am seeing almost all the exchanges are having similar functionality and there will be no big complexity across exchanges. If you get familiar with one exchange then I believe you can use any exchange without any difficulties. Ease in trading platform cannot be a criteria in my view.
But, having good support for trading environment like enabling traders to have lots of technical indicators and providing them versatile charting tool kind of things will be attractive to choose one particular exchange for trading in my view too. But currently most people are choosing exchanges based on trading volume and availability of one trading pair.