Yeah, so difficult to choose!
I also thought of best non-romantic relationship, like friends, or mentor-student, or parent-child, could also be fun.
Tbh, OP is traditionally not allowed, and I can understand why - I have seen tons of threads in the manga section on "best ships", "best fight", etc. I usually take something new from these competitions, learn about new series or get reminded of something I like, plus OP has an edge of having too many fans here compared to other series, so I'd probably ban OP again.
As for the couples, I'd torn tbh. On one hand, I prefer canon ships to avoid unnecessary conflicts (shudders after remembering Naruto and Bleach shipping wars), on another hand, adding some space for one-sided relationships could also be good for a discussion. I need to think of it. What would you prefer?