Sakura. He and Karin doesn't even have any emotional development together. All Karin does is rub her chest against him and squeal whenever Sasuke's around. While Sakura has had annoying Kyaaa-Sasuke-kun! moments, Sakura has made it clear that she loves Sasuke -- and not just crazy infatuated with him.
Sasuke also opened up once with Sakura ("Thank you.") And from what I see, he never even hugged back or smirked at Karin.
Anyway, I think it's too early to be speculating whether it's SasuKarin or SasuSaku since only Karin has met the goody-Sasuke again. Might have to watch out for Sasuke and Sakura's meeting, to be fair.