As of this writing, my favorite editions remain 3.5 and Pathfinder, for one big reason: character creation. I find that 3.5/PF deliver the most ability for PCs to create the character they want within a fantasy world framework. While this is sacrelige in many OSR circles, I like feats and skills as presented in 3rd Edition and its progeny. Is 3.5/PF perfect? No -- the oft-stated objections (rules bloat, wargaming feel, challenge rating/build-the-adventures-around-the-PCs, the power curve, high-level play wonkiness) are mostly valid in my experience as a player and DM. But that sweet spot (say, level 3-10 or so) was awesome.
I have gone back and reviewed many of my Basic Set / 1st Edition materials, and downloaded and reviewed several of the carefully-crafted OSR retro-clone products, including Labyrinth Lord and Joe Bloch's Adventures Dark and Deep. I value the original and OSR products for their relative simplicity, flavor, nostalgia, and sense of real danger to the PCs. However, I like a product with a little more meat on the bones, particularly regarding skills and adjudicating non-combat actions. Adventures Dark and Deep has taken the step of adopting a alternative skill system based on xp expenditure that is partially tied to ability scores -- thus, for many of the skills, it is cheaper to train if your best ability score is that skill's prime requisite.
Mixing and matching these elements then, as Monte in fact says he is doing, my fantasy 5th edition would look something like this:
- Same core design re: six ability scores, hit points, saves, armor class, etc.
- Feats, or some mechanism to customize characters to provide unique abilities
- Skills or ability check modifiers to allow resolution of non-combat actions
- Ability to run 0/1st edition style gameplay (i.e., battlemap/miniatures optional) for quicker play
- Flattening of the power curve
- Deadliness -- the game needs to be dangerous
- Rewards should go back to pre-3e: xp for treasure, to encourage alternate means of "winning" other than monster-slaying, which begets the Challenge Rating/match-the-encounter-to-the-PCs thinking.