I just listened to the last 15 seconds like 8 times in a row, and I'm pretty certain its Amber (and major props to her for hitting it, because that is definitely a Lea Michele note!). The only reason I'm pretty certain is because Kevin's also vamping at the end, so I think it would make the most sense for the two leads to be featured up front and doing their thing. Plus, you can hear Lea's vocals mixed in with the girls in the background, and I can't pick out a time when she breaks out from that. So yeah, go Amber!
I like this version, I think it goes on a little too long, but they'll probably cut it on the show anyway, so whatev. It seems like a very Glee club-ish song, so, awesome!