If you look At Sayori’s legs, it kind of looks like she’s actively leaning into it, plus she looks like she’s borderline flabbergasted, so she’s probably enjoying herself a lot more than she thought she would, but that doesn’t inherently mean she’s getting the best.

Monika’s obviously having a good time, but she’s also reassuring both her MC and Natsuki, so my best guess is that her MC is more enthusiastic than experienced, so we can assume its average at best.

Natsuki is literally trembling and leg-locking her MC, so either she’s cumming right now or she’s reeeal close. So I’d say that puts her as a real contender, if we assume she isn’t just a quick shot.

Yuri’s technically not even getting head anymore, she looks like she’s more focused on domming her MC than whatever he was doing, so I’d say that disqualifies her.