I don't think either have "air superiority" as such.
Just from the reports I've seen, Ukraine are probably better served, in that their air force is based in Ukraine, and they have transportable air defence assets, which they can put anywhere. The russians meanwhile are largely based in their own territory, so it's a longer trip to use them, and over Ukraine territory they are quite vulnerable to hand launched missiles, and that has been borne out by how many they've had shot down. Their air defence can also only be in occupied areas, so has limited value unless Ukraine are flying over that territory which I'm sure they do sometimes.
It surprised me at the very start, that the russians didn't take out of action more airfields/aircraft, this is normally what you do in an invasion, but that might be because their initial intention was "Kyiv in 3 days", and they wanted to use them after they had fully taken over, seemed a big mistake to me. This (imho) allowed Ukraine to position their air force in more distant airfields, making it more difficult for russia to attack them, as they don't have high accuracy missiles to take out aircraft, and a runway can be repaired quickly.