IMO Neither one.
You cannot compare Fallout to TES (more specifically the first two ~the latest two are none too different from TES)
These series are as different as apples and orangutans. Both do what they intend very well, but neither does well what the other intends.
(Until FO3

, which IMO switched intents, and exceeds TES4 at its own game, but not TES3)
**Unless you are only talking about Fallout 3 and NV, it depends on the idea of "best at what?"; along the same lines as "what's the best tool, a drill or a pipe-wrench?".