There isn't really a best pairing because pairing for one unit may make another one suffer. If you wanted the best Lucina then MUxChrom would make that but it would prevent you from getting rightful king inigo in the process.
You are incorrect. Sumia!Lucina is better than Olivia!Lucina.
Despite Sumia being a complete Scumbag and Best Friend Backstabber she's the next best choice after FeMU for Lucina.
Cordelia x Lon'qu has great supports and they compliment each other so well for Super Severa.
Stop calling Sumia a backstabber already. We get your point already!
I say it as it is. I care not if there are those here that support NTRing your best friend like Sumia does.
There is no evidence that Sumia willingly backstabbing Cordelia. Do they even show that Sumia knows that Cordelia likes Chrom? Does Cordelia know that Sumia likes Chrom? (Their support conversation mostly talks about Sumia doing the flower petal reading and some of Sumia's confidence issues, nothing about who they have crushes on). We can't just make presumptions that Sumia is a backstabber and a complete scumbag just because she is a friend of Cordelia who happens to like Chrom also.
"I will speak my mind and say what I want and if you don't like it, well too bad!" "And my Pikachu pillow says hi"