Going to go with David and Jeff, and Jeremy and Sandy.
David and Jeff seemed nice enough, but out of all the teams that made the final 3, they are the only ones I tend to forget. they didn't get much screen time, they were overly likable or despised, they were just sort of there.
Same goes for Jeremy and Sandy, though I remember them a bit more because it's a more recent season.
I base this mainly on the fact that both teams reached the final 3 without much fanfare, there wasn't much to go off when it came to them, they both seem nice, but they aren't memorable at all. I expect some low-placing teams not not be as remembered, they weren't around as much, but when it comes to the top 5/6 in each season, most people remember them and have developed opinions on them, these two seem almost too generic.