It depends on what it is you're meaning, but typically when you're going for an exchange where you're going to be trading Bitcoin back and forth, you want to find an exchange where there are small fees and the difference between the buy and sell orders is quite small. This is especially important if you're trying to capitalize on small market movements instead of macro movements that can take weeks or longer to happen.

I personally don't have a preferred platform because each of them are good in their own ways and each platform has their own pros and cons.