Imaro
Legend
If I were to take a stab at it: I would say that "what's best for the game" would be whatever helps best realize the creator's vision. I might not like that vision, and creatives are definitely capable of making decisions that don't have a positive impact on their own vision (from personal experience), but any other definition is rife with issue. Having said that, what's best for something as a creative expression and what's best for it as a commercial product are frequently at odds, and I understand a balance needs to be struck.
I don't really enjoy what WotC has done with D&D in so far as a game engine. I've been generally positive towards the fluff they've put out, and the larger variety of voices and cultures in their products is great to see (missteps aside). They may no longer be making the system I want to play, but I can say that I believe they've done a fantastic job at growing D&D as a game and as a brand. Even if I don't really like the system they are making or the company itself.
But D&D doesn't have one creator. So how do you measure it then? Again, and this isn't a dig at you per se... but it seems like because there's no singular source for true vision... it boils down to what's good for the game is what I want personally.