Nittaku "Premium" 3-star balls are the best for tournament/matchplay. They are the only ones made in Japan (and not China), and they even play on that fact in their advertisements x]. I like them because the batches are really consistent. I don't think they're magic like some people see them, nor am I picky about how you always HAVE TO play with that ball in tournaments. Other brands are good, but I've seen way too many 3-star bad batches (maybe even fake copies of them). I think I got some fake 3-star BTY balls with soft spots and inconsistencies too xD
But Nittaku Premiums are hell-a expensive. But you pay the price for quality (excuse me "premium" quality xD). If I were to get training balls, pretty much any cheap Chinese brands would do. DHS, Double Fish are some examples. I heard rave reviews about Gambler balls, but I tried the Gold-version (two-star I believe, Platinum is the three-star version), and I can honestly say that Gambler is one of the first balls that I HATED. They were so inconsistent, not evenly hard, and the powder on them was nasty. It was a bad experience for me (could've been a bad batch, but I doubt it...still, that just means that the balls are inconsistent between batches Dx).