When you take a step back and look at them individually you realize they aren't very useful unless they're a package deal. Someone with super durability but no super-strength makes an excellent human shield but when it comes to fight may rely on his opponents tiring out from hitting him so many times. On the flip side all the super-strength in the world won't mean shit if your bones and muscle are too brittle to support the weight you try to lift.
I'd say super durability.
Even if you say strength allows you certain durability qualities like being able to support what you are lifting and not hurting your hand when punching, etc.....you are still toast if you drop something on yourself or your enemy shoots you or even punches you and knocks you out. Durability---you can still pack weapons, a jet pack and what-not and move around well and fight well and not have to worry about crashing or being hurt in return.
Durability- when you fight some one at much higher levels of strength than you you cant hurt them because your too weak. but they cant hurt you because of your durability. the only thing to do is let them get tired.
or have weapons like guns
Strength. you will be very powerful but anything and kill you. but then again you can wear bullet proof vest