Definitely AC Odyssey. I was seriously considering to vote Odyssey for GOTY 2018 instead of GoW, but then again, GoW had some amazing moments that made me choose it over Odyssey.
Origins was the first RPG style AC, and I think that decision was something very important. Older AC games started to become repetitive, same story, different setting. Odyssey was a much more polished RPG than Origins. Later they added more boss fights with mythological beings in free updates, grinding to lvl 50 to just fight Medusa was something did without reconsidering too much.
All in all, I really enjoyed Odyssey being an RPG, but probably the most important reason was relaxed atmosphere, the graphics were vibrant, and the music... That's something I'll miss in dark AC Valhalla.