I've used Gama Pressureless, Penn Pressureless in practice. They either lose fuzz or bounce fairly rapidly. The Tretorns last for months and months, keep their fuzz and bounce. The big X makes them easy to identify on the courts. Best value for practice tennis balls around.
I bought a ton of these over ten years ago for my ball machine and practice. Then I fell out of tennis. Now I'm back and these balls are still the same! Great bounce. These balls are magic. If you need to save money, a can of these will last you until you beat the covers off. I cut one open and they have some sort of crystal like foam inside. Might want to keep away from dogs.