Highway driving is always best for your car and your cars engine.
When you do a lot of highway driving your engine can reach operating temperature which helps keep moisture out of the engine oil and also prevents sludge buildup.
When you do just city driving mostly then your engine will not get up to complete operating temperature to burn off the water that can be present in the oil and you get a lot more sludge buildup.
City driving mostly is the worst thing a car can have done to it when it comes to extending the lifespan of the engine.
All that stop and go driving is not good for the engine or transmission either.
You also wear your brake pads or brake shoes out faster when you have to press on the brakes often to stop which you do more of when you're doing city driving.