Using your excellent criteria of douchebaggery, I’m going to go with “With You I’m Born Again” because he likes to pull out the Christian card too.
Does someone have a handy list of birth years for all the contestants?
I want to hear Adam do some Queen - Fat Bottomed Girls, maybe? They’d never allow it, but I think he would be great!
Okay, so Google tells me that Allison was born in 1992.
Hmmm…Out of the top 100, I’d guess “I Can’t Make You Love Me” – but the judges would say it’s too old for her. Maybe she’ll go for “Damn I Wish I Was Your Lover” or “This Used to be My Playground” (can they do Madonna?). I think “Walking on Broken Glass” would kick ass, though.
“Baby Got Back” would be pretty cool.
Per Wikipedia:
Danny - 1980
Adam - 1982
Lil - 1984
Scott, Matt and Kris - 1985
Anoop - 1986
Allison - 1992
How about Gokey doing “Another One Bites the Dust”? ::shudder
Lucky Lil - she gets the best year in the history of rock and roll. Too bad she’ll blow it, even though she could do “What’s Love Got To Do With It”. She’ll probably do “Automatic” by The Pointer Sisters. 
I dare her to do "Cum On Feel the Noise’!!
I hope Allison has a good week. I could see her doing “Life Is A Highway.” Or with the right arrangement, “November Rain.” That one might be too risky though.
I really, really want Anoop to come out and sing “Rock Me Amadeus.” With the wig and everything.
Too bad Adam wasn’t born in 1984, he could do “Karma Chameleon”. [snerk]Maybe later in the competition if Boy George is a guest mentor. [/snerk]
“It’s raining Men” charted in 1982, but I don’t see it on the top 200 for the year. That might be a little too on the nose for Adam, but it would be hella fun to watch him perform.
I hope Allison does “Smells Like Teen Spirit.”
Never allow it? How soon we forget…
I would vote for him until my fingers were bloody stumps if he did that.
My guesses/hopes:
Danny - “You’re The Biggest Part Of Me” by Ambrosia because he can really douchebag it up.
Adam - “Let’s Groove” by Earth, Wind & Fire. I really, really would like to hear this.
Lil - She should do “What’s Love Got To Do With It” by Tina Turner; she’ll probably do “Automatic” by The Pointer Sisters because she just can’t pick songs. (Sorry about repeating myself.)
Scott - “Like A Virgin” (Hah! Just kidding!) No, he’ll probably do “You’re The Inspiration” by Chicago.
Matt - “Careless Whisper” by Wham!
Kris - I can’t peg this guy. Throwing a dart at the board, I’ll say “All I Need” by Jack Wagner.
Anoop - Since he wants to be Usher, I’ll say “Dancing On The Ceiling” by Lionel Richie.
Allison - “November Rain” by Guns N’ Roses. - I had this picked before I saw your post, SaharaTea - great minds think alike!
It would be really tough to condense “November Rain” to a minute and a half.
But merciful (dislike the song). Meet you guys here Tuesday…
Why, yes, that was quite forgettable… 
“Aw, down beside that red firelight…”
He sucked all the fun outta that song…