I'm always surprised when people don't have OTPs in fandoms they've been in for a long time. ^_^ I tend to be your opposite, though. It's the main characters I usually feel more compelled to pair up in OTPs than the minor characters, except when there's a large cast (like PoT, Bleach and Naruto).

It's fun to analyze our preferences. ^____^

Ukitake and Shunsui (BTW those last two definitely belong together)

You won't get any arguments about that from me.