I chose 2nd Edition. I was quite happy running my first true campaign in 2nd Edition, so I know I could make it work for the long haul. I also uncovered by old 'Keep on the Borderlands' module for 1st Ed, and reading through it has made me realize how strange that system was. Still, I have to admit, I am curious as to how 1st Edition would work in a campaign...
That said, I'm sticking with 4th Edition for the forseeable future. I can't wait to kick off that campaign.