Wow. I'm VERY surprised I have not responded to this yet...
Obviously, the original is going to get my vote. While I think the remake was a decent attempt, as well as one of the better remakes of any film, it failed in one area -- the look of the film. The original Texas Chainsaw Massacre has that grainy, home video look to it, which makes it scarier because it influences you to think, hey, these guys are just filming what is happening. In the remake, as brutal and cool as it could be, you always had that fail safe of, oh, it's just a film.
Part 2 is... hard to swallow, if you've seen the original. I think it's worth a watch, but that's about all I can say about it.
Part 3. Been years since I've seen it, but I seem to remember liking it.
Next Generation. Aside from seeing some big name stars in their early years, it has nothing really redeemable about it. The final half hour is worth seeing once, just for the sheer ridiculousness of it all.
" There's no such thing as fair or unfair in battle. There is only victory, or in your case, defeat. " - Vegeta