Re: RPMFusion Vs UnitedRPMs
If you don't need UnitedRPMs use RPMFusion. I think UnitedRPMs has some extra packages, but RPMFusion have some greater expertise, most of the people maintaining packages for official repoes are also behind RPMFusion so fewer collisions are possible. There were times when RPMFusion was undergoing a infrastructure reorganizing, so it was lagging behind with packages for few Fedora releases, but that should not be an issue anymore.
In any case use only one or the other, these two are not compatible.