I think Ephraim's is slightly more challenging and... Fire Emblem like... because it focuses on the war aspect, and almost all Fire Emblem games focus on war (excluding FE7 and parts of FE10). I didn't take much interest in Eirika's story as far as plot goes. Carcino didn't really appeal to me and I felt that Eirika was too much of a weak, helpless character who tried to act tough. But maybe that's just the impression I got.
Knoll was preferably over Innes for me. I do have to admit that Eirika's maps and playthrough was interesting though. Carlyle was cool for sure.
