I only use new balls, unless I am giving a lesson one of my neighbors kids (I used pressureless balls for lessons). Reason being that the people I play with are very skilled and we usually shred through the felt within 12 games. When rallying or practicing, the felt goes even quicker.
ATP career high ranking of #854. Donnay Mids Gut/Poly.
Give me a racquet and I'll find a way to win!