Heirs of Fate because it actually knots the whole parallel/pocket dimension story mess together in a decent way and being enjoyable as a whole.
Seriously though, I just finished the whole lot of Fates and imo it goes:
Storytelling: B>R>C
Gameplay: R>C>B
Difficulty: C>R>B
Characters: wat (there's lovely and awful on both sides, except Valla which i- wat)
Birthright was a breeze, but that's okay because it was nice once you got into the flow. I found the story well told and on that route things just fell into place on that front, largely typical and not so intuitive, yes, but nice all the same.
Conquest was... everything but a breeze, though that did give me a way bigger sense of accomplishment. On the story front I facepalmed so very hard up to ch.22 or so, after that I guess they tied the rest of it up rather neatly in comparison. The maps were overall more creative and I liked that, although it sometimes went too far into bs territory imo (looking at ch.10, ninja rape cave and the stairway in particular). This route I enjoyed being done with the most lol.
Revelation was probably my favourite. All the cast together for your army, except a few I guess but that's where the unit logbook comes in. Maps were looooooooong which made it tedious at times. Story is the canon option, so I guess that works in its favour. Major points deducted for burying the biggest revelations in DLC though.