Dunlap – Years ago, I used to swear by Dunlap Grand Prix balls. I loved the sound the made when you struck them solidly; and they lasted longer for practice balls than anything I ever found.
But I also found them hard on the arm. Seems like the thing that made them sound good and last longer also made them cause more vibration through the arm. My local Florida tennis pro used to use them as his teaching ball; but switched due to arm problems (which then went away).
Wilson – Many tournaments use these balls; but I find them livelier than I like; and they seem to fly a little off my racquet.
Penn – You can usually find “regular” Penn balls on sale somewhere for $2.00 to $2.50 a can; and they are good balls to play with.
But I have found that the slightly-more-expensive Penn ATP ball is just a little better made, has a reasonable bounce, and lasts just a little bit longer than the cheaper ball. They are tough to find in the stores; so I normally buy them online by the case (at about $2.50 a can) through Holabird Sports in Maryland.
So I guess for me, the Penn slogan is true, “The Ball Matters.”