Ok, I'll do this by CD, since I can't think of a particular song that sticks out as being my least favourite...
LOTGA: She's Got a New Disguise, I guess, although I do like the song. I like the whole CD, so it was hard to choose.
Underdogs: Invasion 1, Rico
Beautiful Midnight: Hello Time Bomb, Load Me Up... arguably because they were so overplayed.
Audio of Being: I don't have this CD handy so I can't judge right now.
Avalanche: A Long Way Down, Bright End of Nowhere... not terrible songs, just really drab compared to the rest of that amazing CD.
WLRRR: North American For Life, Poor Man's Grey, Put Out Your Lights.