If I had to pick canon couples then it would be Kogorou/Eri That couple is really nice, they really need to get back together.
I'm not much of a ShinRan fan (Have a feeling some people will kill me for saying that)
KazuHei is hilarious
AoKai is cute too
HakuAkako maybe?
As for BO ones, Vermouth/Gin seems interesting.
Bourbon/Sherry(Shiho) is another one.
Depending on that person's gender and identity, AnokataXVermouth
Yaoi pairings:
ShinKai (note not KaiShin )
KidXHeiji (It just seems right with their personalities)
HakuKai
Random crack that could happen :3 --> SpiderXKid /shotshotshot by bullets and cards
And that's all I have for now. My ships usually depend on my mood haha