Path of Radiance for me, also one of my favorite games ever.
RD was a great follow-up, and tied up all the loose ends well, but it had some pacing and narrative issues that kinda bugged me when I look at both as a whole. I was also annoyed at some of the prerequisites needed for key story elements..though it's certainly not a unique complaint for Radiant Dawn. I found Path of Radiance really benefited from following one character's story arc, rather than jumping around several.
For reference my FE ranking is below, if anyone is curious how much our opinion overlaps:
1.) Path of Radiance
2.) Blazing Sword
3.) Radiant Dawn
4.) Fates: Conquest
5.) Sacred Stones
7.) Shadow Dragon
Still need to play through the other Fates games...and eventually I'd like to play some fan-translations of the others. Haven't gotten around to it though.
NNID: Zephyr25 / PSN: Zephyr--25 / Switch: SW-4450-3680-7334