Britney, definitely. Almost everyone I work with disagrees about this for some reason. I figure only the ever-so-insightful Teeming Millions can vindicate me on this one!
(Yeah, yeah, Christina can sing better, but we’re not talkin’ talent here, if you know what I mean.)
Both 
I would also have excepted:
Yes.
Britney… positively Britney.
Actually Christina has a decent body but that nose…
If those are my only two choices, I choose “Gouge my eyes out with a fork.”
I don’t understand what the question is supposed to be. Does it begin with, “If you had a gun with only one bullet…” by any chance?
If I were to be extremely intoxicated and my lesbian seducto-vibes were at full force, I can see the following scenarios:
I bed Britney. We’re getting into the foreplay. I touch her breast, my hand bounces back violently because of her implants, and I accidentally impale myself.
I bed Christina. She makes incessant jokes about “unbottling her genie.” When she reaches orgasm, she hits a high note, causing my eardrums to shatter.
I’ll take my quiet girl, thanks much.
I suppose I’d have to go with my fellow partial-Ecuadorian, though I can count the songs I know by the two of them on my smarting ears.
Ohmigod, guys, like, JC from *NSYNC is soooo cute! I used to like have the total hots for Nick from BSB, but he starting dating some, like, total skank! So I got like a major hot attack for Justin from *NSYNC, but he’s totally dating Britney! Like, I bet they tongue kiss and stuff! And I went to their concert this summer and his hair was so in dreadlocks! And I’m all like, Justin, you are such a hottie but what’s with the hair? So I totally couldn’t like him any more! So now I’m all about JC. He’s like the cutest, even if his teeth are kinda nasty, and he like totally can sing, like for real! And he was on the Mickey Mouse Club! Ohmigod guys, that’s the kewlest! Like I totally loved that show when I was 4!
Ohmigod, guys. Do you think JC would date someone who’s 12? Like, I totally think he would date me. I’m like totally better looking than Britney. And my boobs are totally real too, I just got my first training bra!! :D:)
And, like, I’m totally waiting till I get married to have sex, like Britney. Like I think God is the coolest and I waan save myself for him!
Ohmigod, gods, like do you think JC’s dating Christina Aguilera? They were so on MMC together! Like, what do you think?
Gotta take Britney, I’ve thought she was a cutie ever since the first time I saw her.
Vanessa Amorosi
Oh, wait, I know:
Christina Aguilera has more upper body strength than Britney Spears. Plus, she has the reach advantage. Definitely, Christina in three rounds.
Rape me with a weedwhacker please.
Cristina hands down (or on). She is sexier, I love the petite ones. I could care less about the music.
If I only had one bullet, I would run to the side and attempt to get both of them.
You then need to go for the head shot Hastur. There wouldn’t be much to block the flight of the bullet.
If that failed I’d do Brit. 
I’ll second that. And third that to.
Not that I enjoy the music of either very much, but I can tolerate Britney. Christina’s voice irritates the hell out of me. All that damn vocal cascading…PICK A DAMN NOTE!!! These people (modeling themselves after Mariah Carey) think that if you can change notes quickly you must be a good singer. It drives me nuts. (MC included).
Jman
Britney is hotter, sexier, and her music is better.
In short: Britney is a goddess. Christina a cheap whore.
Case closed.
FWIW, my ranking of hot, young, pop music stars:
Brit
Mandy
Jessica
Christina
Dear Santa: I want to suck Britney Spears’ implants this X-mas. Please?
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Christina on the bottom, Britney on top. Oh what a meaty sandwich that would be…