I think Iuno is the hottest wuwa, and it's not because of my investment in her. I have both Iuno and Zani at S0R1, and I believe Iuno is hotter.
Even though Zani is objectively hot, Iuno still wins. It probably is because Iuno's panties are her hottest trait for me. The way she lets you take a peek at her panties in every animation is extra hot, and while some may think her skirt is censoring her, I think it only adds to her charm.
Really, Iuno is the only wuwa I've ever thought I've wanted to marry.