She said this recently when she appeared on Andy Cohen's show Watch What Happens Live.
Her exact quote: "Britney because she dances."

Here is the vine of her quote:
https://vine.co/v/OIj3xMmV1O3

Still mad about the idontknowher.gif I see

TBH I would too. Only because at the Britney show I would have fun. at a vocal emphasized show I would need perfect vocals. and Celine does that. Mariah sort of is a hit or miss with her vocals so ya. this does not change the fact that her songs r amazing and I'd love to hear them live though.

It's not like Mariah knows ha anyway

Same. Mariah's too good for Vegas. Mimi must still have her pressed.

I'm sure Mariah will be very bothered

She wasn't even being shady. JLo isn't a petty person. She was just answering honestly.

Well. It's true

I'm a Britney fan who doesn't want to see her perform but I agree... I'd rather watch her perform than watch Mariah.

Exactly. She wasn't trying to be shady.

Ugh stop with the overanalyzing and finding shade in every comment.

JLo's jealous of Mariah's big big booty

Agreed. Why are people so mad?

@ Britney cause she dances. She does WHAT now

And.....?

J.Lo ha revenge