So, a non-WotC version of D&D?
Given my favorite edition is 3.5Ed, it would have to be one of the major clones. While I love some of the aspects of several of them, like FantasyCraft, Midnight, True20, Arcana Unearthed and others, the key feature of 3.5Ed that makes me love it so much is it’s flexibility of character design. Because of that, there’s only 2 I’d consider: Pathfinder or Warriors & Warlocks.
Pathfinder approaches the depth and variety of options 3.5Ed. But Warriors & Warlocks, as a supplement of Mutants & Masterminds, has the systemic flexibility to design PCs as I see fit, mimicking the options across 3.5’s myriad sourcebooks.
…and in other editions of D&Ds well.