About three years ago, close to when I first started this blog, I decided to restart my Greyhawk campaign.
I was, at the time, faced with a decision as to which version of the rules to use. I had played the game with the little brown books, "the box with the red dragon on it" (Holmes), AD&D, and 2nd Edition. Honestly, the system I knew the best, by virtue of simply having spent time playing it, was AD&D. To this day, I can run a game of AD&D off the top of my head with no problem. I might get an armor class off by 1, or forget some trivia about a spell's duration or something, but really, I know it inside and out. 2nd edition is a close second; I completely bought into the idea of kits, and I bought every single damn one of those "Complete Player's" books. I ate them up.
But when it came time to restart my campaign, I agonized for weeks over whether to use the original LBB's (plus Greyhawk, Blackmoor, and Eldritch Wizardry) or AD&D. As far as I can tell, from a practical standpoint, they are pretty much identical. Oh, sure, there are a couple of differences in particulars, but on the whole they are functionally the same, if you include the supplements to the LBB's. AD&D is better organized in some respects, but in others it is very much as a clugey set of rules as OD&D ever was.
And here I was, making my choice for my own game. If the rules themselves were pretty much the same, what made the difference? Honestly, I had two points of contention:
I knew AD&D inside and out. I can play it without the books if needed. I know how to house-rule it without even batting an eye. I still had my books. It was an old lover to whom I could come back in perfect comfort, and I knew all her tricks, and she knew mine, and we loved that fact. On the other hand...
I like to play in my FLGS. Playing with the LBB's would just make all the 4E-playing drooling slacktards' jaws drop even more than seeing the DM screen from AD&D. I honestly didn't care about the mutability and "rules lite" sense of D&D, since I can make rules changes to AD&D just as easily.
So it came down to what I knew better. I could get as much of a "wow-- they're still playing that!" factor out of AD&D, with the added bonus of not having to re-familiarize myself with the rules. I know; I'm a petty, petty man. But I'm having a BLAST running my game!