Roof Piece had more meat to it but I’ll always dislike the way Oda handled Big Mom on the roof. It was really a 1.25 vs 5 instead of a 2 vs 5
Kaido was dropping people off and engaged in actual direct combat with each supernova. Big Mom would occasionally pop in for an attack here and there that never did any damage. She felt like Kaido’s subordinate instead of his equal (with Kaido calling her pathetic and saving her)
God Valley’s conclusion is more meaningful but there wasn’t a real full fledged fight due to Oda’s weird tendency to avoid drawing full exchanges in flashbacks. It was more Marineford than Onigashima
I think overall I’d actually say I enjoyed God Valley more because of Rocks. He’s truly a larger than life character and his death still saddens me
RoofPiece had sick moments (Luffy tapping into ACoC, Zoro using Asura for the first time in like 500 chapters, Zoro blocking Ocean Sovereignty, etc) but Big Mom was irrelevant and Kidd/Killer didn’t contribute much to the fight itself. Though I’ll admit them going off to take on Big Mom was pretty cool
I’d say I’m torn on this now that I’m really sitting here thinking about it