Personally I would've picked Youko, she has it all together.
Ritsu's nice and everything (those stockinged legs *chef's kiss*), but if it's forever I want someone stable.
@Northern Ritsu already fits into his life though, and doesn't just complement it, but consistently improves it. The earlier chapter about the day off showed it. Yuko is an unknown variable, attractive and intelligent, but untested as a homemaker. Also dealing with her pervert of a father would immediately make me think twice.