That is tough because it incorporates many factors, some subjective, some not. For example, my Roland BK-9 had all the potential to be a great sounding keyboard, in spite of it's two small windows that had a purpose. The trouble was that the factory released it without balancing the thing. That, of coarse, is the factory's fault. Then you have Yamaha that almost never sends anything out unless it's right, but I think their drums are whimpy. That's subjective, as home players don't think so. The Ketrons, e.g., have arguably the most realistic. live sound. but has been known to have a few other flaws in the beginning. My Pa4x is the closest I have seen yet, but even they had to send out some updates to fix a few minor items, but made up for it by a major upgrade.