This barely started and I'm already 100% on team Fuukatsu, like other people here. A poly ending would be a little bit boring to me, almost like choosing nobody (nothing against polyamory itself, do whatever makes you happy IRL).
My ideal ending would be something akin to what another person said, with there being a twist that some people's "love" is actually just "the kind of love you have for a friend, but very strong" and that she can't differentiate it right now, which is why those couples she set up in the past broke up. That way Sayo wouldn't be "turned down", she would just reveal she doesn't actually "love love" Mei like she thinks.