I just finished Path of Radiance and kind of wanted to talk about the series.
Mine would probably be Blazing Blade or Mystery of the Emblem, BB because having some weird cult terrorist group as the villains was more fun than Evil Nation nº12837, MotE because i think it has some of the best gameplay and maps of the franchise while having a way better story than the other newer FE games (that i have played, Awakening and Fates).
I know a lot of people don't like this one, but for me it's Fates: Conquest. A story about the bad guys, who are portrayed as a group of siblings trying desperately to please their father who grows more demanding and irrational with every passing day, was immensely more compelling to me than "bad country is summoning monsters".
It also helps that the gameplay is super tightly designed. There's no ability to level grind in that campaign, so the designers were able to carefully map every single battle out.
the gameplay in fates is great. and i really like the premise, but they just didn't pull it off (at least for me, obviously it worked for you.)
spoiler
i think we might have had this conversation before, and i think i said i hadn't played it while paying attention to the story since it came out, and that's still true, so this is mostly half-remembered and based off the vibes more than anything else.