In Conquest, specially in Lunatic, Effie, Azura, the royals, and obviously the Avatar are the best of the bunch. Arthur early on is a good unit but his terrible luck makes him bad on the last chapters. Beruka is a mini physical Camilla and that’s good overall. Niles starts good and he can be a good mage killer but his strength stat will fail you later on.
Silas is in Xander’s shadow and he doesn’t offer you much to be honest. Mozu is hit or miss if RNGesus fail you on the level ups, If RNG is on your side, though, give her the dread scroll to make her near unstoppable. Charlotte is garbage early on but if you manage to make her a berserker and give her a good balanced weapon between hit and crit she will consistently spread lethal punishment to the competition.
Odin and Nyx aren’t really worth it in my experience. Laslow is better as a Hero and Selena as a Bow Knight. As for the second generation I think it really depends if you want min-max or simply enjoy pairing more. For that I think you should look for pairing statistics to make the best bloodlines.
Felicia /Jakob are your best cheerleaders on pair-up, but compared to Awakening, pair up is more balanced in Fates so you have to be really careful in tricky maps like chapter 10 to tank certain waves of enemies.
That’s all I can remember. It’s been like four years or so since I last played Conquest.
Revelation is a harder Birthright. That’s it. You can be more lenient with min-maxing since you can grind at leisure.