Daggerfall it's a damn good game indeed. I remember reading in one thread that a newcomer to the series was feeling "overhelmed" by the sheer ammount of content in Skyrim. Hell, I could barely keep up to my schedule in DF. Big, open world? I did never, and never will, be able to visit each single city and settlement in DF, let alone each dungeon. Radiant story? Pfft.
But I don't really think that I have a "best pf the series" one. It's like having a lot of children, some of them may have serious issues, but you love them all.