Oh boy, I've done a couple of runs. I didn't grind most of them (my first lunatic run and my lunatic+ run), but I have one file of Lunatic I grinded to do apotheosis. I built my pairings around predetermined goals, but this is pretty much it.
I had these FeMU pairings.
Avatar x Walhart- Lunatic was easy as shit and I was pretty happy with waiting for a Morgan with Conquest.
Chrom x Olivia- This one kind of gave me a mediocre Lucina, however the Inigo from this pairing is very powerful as a Dread Fighter or Swordmaster. Inigo is generally a beast with Rightful King.
Lissa x Vaike- I did this because I was going for a Dread Fighter Owain, personally I believe the Hero/Dread Fighter line are Owain's best options.
Maribelle x Henry- Maribelle has some interesting supports... And only a few of them really work to produce a good Brady. It was between Henry and Libra, and I decided that Henry was better for Maribelle and Libra for Tharja.
Sully x Virion- I think Kjelle is generally one of the worse children due to Sully's awful stat modifiers, so I threw Virion over here since I had nothing better to do with him.
Sumia x Gaius- This produced a pretty fast Falcon Knight Cynthia, which was my goal.
Cordelia x Lon'qu- This is probably my most powerful setup and one of my favorites, since both of the parents have good modifiers. I went Assassin Severa and she turned out as one of my best units.
Cherche x Stahl- I think Stahl has the highest defense modifier out of the possible pair-ups for Cherche, and since I wanted Gerome as a flying tank, I used this setup. It works well.
Panne x Gregor- This is another very powerful setup for Yarne outside of his Taguel class. Gregor has some great modifiers for stats in general, and this one ended up as the best.
Miriel x Ricken- This is one of my other powerful setups. This is honestly the only viable setup for Miriel in my opinion, because Ricken doesn't do well with many other supports and the two powerful mages going together produces a very scary Laurent. I decided to build him for Magic only as a joke, so when the build finished, I capped at 72 magic (with limit breaker).
Tharja x Libra- This is a good Noire setup for using her as something other than her base class, since Libra has great modifiers and complements Tharja's well. Libra is also here since I used Henry for Maribelle.
Nowi x Donnel- Nah has a tendency to lag behind without Donnel as a father, and she's an absolute monster when she caps everything. Currently my standing best unit made from pure statistics.