My favorite version is 3.5. I was introduced into D & D by a friend that had an old 2nd edition. (Wheel of time) I have played those two versions plus 4th edition. My order of preference is 3.5>2.0>>>>4.0. I really like the depth of detail for 3.5. I like to be fully immersed in my character and love detail. 4th edition just isn't D & D to me.
I am still a AD&D fan and enjoy it a lot. Second choice is still going to be 3.5 as I learn more and more about it. Being a Dungeon Master in 3.5 helps a person do and learn a lot more. I am always doing research as to what I am going to have the party experience next to keep them all wondering what is next.
It's got to be 3.5 for me, followed by 2e and OD&D. I don't much like anything after 3.5. I've been playing Dungeons & Dragons for quite a while now and I've seen it change. I remember how much I liked Unearthed Arcana. I took a bit of a sabbatical in the late 90s and played L5R... And then Dungeons & Dragons and L5R merged for a time. Those were good times for me. Of course, I was in the Army and the campaign I ran was interfered with by 9/11 and spending a bunch of time overseas. And now I've found this site and it looks great! I'm even thinking about starting a Rokugan campaign… maybe.