Tough one.
I'd argue that the modern Tweakers, Hobbyists etc have exceeded the performance of the old classic Tuners. So to get the best tuned springer may no longer be a one-stop-shop (it never was, but the custom shops where a good starting point).
Best to me is a combination of inherent accuracy and the easy with which the shooter can repeatedly access that accuracy under differing conditions. When you get it right it's a synergy of the action's characteristics, a great barrel and matching pellet, gunfit and balance of the rifle (which inevitably must include the scope).
Hence the "best tuned springer" can't simply be bought, there's too much variation between shooters to make it possible.