I suppose this is cheating, but when I've finished work on my Twilight homebrew system, that'll about do it for me. Twilight is based on my calculator-crushing Nocturne engine, which despite the mighty mathematical emphasis did everything I wanted it to, especially time management and completely freeform magic. Twilight has the advantage of merely requiring a handful of d6s to do anything, no calculator required.
If I can get the balance right, Twilight should also be able to use D&D stats with a minimum of interfacing. Plus it's completely classless. I'm writing the rules to handle anything, rather than providing a framework to hang hundreds of specific rules off, like D&D does. While that might not be good for a future in publishing, I know it's going to make for good playing.
But if we're talking about systems that exist, and are for sale, then d20 seems to make the most sense to me. It's not perfect, though.