Fi is always my favorite, but for some reason I never liked the pairing with Parja. She's a bit of a cardboard character, and kind of...generic. When she showed up at the end of True Colors my response was something along the lines of "Who are you? Wait, you're the romantic interest? Lol, no thanks, come back with someone more interesting for Fi, he's waited too long to wind up with generic."
On my tolerant, accepting, willing-to-give-benefit-of-doubt days I suspect that's possibly because she was a character for so little time. But she always struck me as "Oh crap, I have three pages left and haven't paired Fi off yet, I'd better make a character solely for that purpose."
My vote was tied between Mereel's, uh..."pairing", and Atin's. There's something amusingly vindictive about a clone turning into a right little manwhore.