I prefer Oz over all of the other love interests in regards to Willow. I loved them together, and was actually disappointed that she chose Tara over him in season 4. In a way, the Tara-Willow partnering made the program less watchable for me (I'm not against lesbianism, I just preferred the Oz-Willow partnering). I would have loved to have seen them get back together at any point, and don't believe it would have been less believable because of Willow's interest in women. She clearly had attraction towards men in the earlier seasons, and I doubt this would have changed so dramatically. Being bisexual means she can explore both sides of it, and makes the ability for her to be with men again completely believable.
I'm still holding out a secret hope for Oz and Willow, despite knowing it is likely it won't happen again.
