3rd. Of course, the tweeked 3.5 is better, and the further tweeked Pathfinder is even better...er. So Pathfinder is my choice, It's just that Pathfinder is functionally a strain of 3rd. Honestly, pre-3rd only has nostalgia. The rules were terrible. Kinda like how Darwins original view of evolution was terrible. Of course it's terrible, it was the first shot, it was still genius for it's time. If you still think pre third was good rules wise, explain to me the difference between multiclass and dual class. And then restate your point with a straight face.
4th is a trickier beast. 4th is still good. It is very simple, and has a streamlined MMO-like feel to be accessible. Its a fine starter. But for an experienced player, it is just not as good. Listen to a battle in 4th, then listen to a battle in 3.5. Now, try to picture the battles in your head. 4th looks like an interesting tactical battle that you would see in a really good MMO. But 3rd looks like an actual, well, fight. I play 4th and I practically see numbers floating up above the characters heads, and selected monsters with an itemized list of debuffs. 3rd, I see a story. And the stories the thing for an RPG, because we have MMOs for our purely abstract, tactical play. 4th tries to set up the entirety of the world that you can interact with to make for a tight, balanced system, but 3rd gives tools for putting some organization to anything you can imagine, gives you the rules to apply to anything. For a Pen and Paper RPG, that's just the better approach.