This is an interesting thread idea. We've discussed to death our favorite songs in the soundtrack, but I don't think we've ever talked about our least favorites.
I'm gonna have to go with Access as well for my least favorite. Not that it's bad, it's just that the rest of the soundtrack is so good, and there's not a whole lot of interesting substance to the song. It's very repetitive and simple, which isn't always bad, but in this case that makes it not as good as most songs in the soundtrack. Next after that, I'd probably say "Charge" (the music when fighting Muscle Doctor). Again, not bad, but very short and repetitive, and not particularly catchy, and only applicable for a very short period of the game's time.
Although I really like Oppression, I can understand why some people might not like it, since it does kind of have that rough and grinding sound to it that some might find unpleasant.
I'm a little bit surprised to hear that Eli isn't too fond of the title/Plantation theme. I always felt as if the strongness of the opening melody is what grabs your attention early on. I still remember on my first playthrough, when things were looking grim and getting ready for the bad ending, going back to the main menu, and being greeted by Quote (whose name I didn't know at the time), and that music starting. And that experience helped solidify that feeling I had of "Oh man, things are not looking good, how on earth am I even going to stop the Doctor? Is there any hope?"