Both use a 120mm smoothbore gun made by Rheinmetall. The Leopard is slightly larger. The US tank uses a gas turbine engine with slightly more published horsepower than the German's diesel. The Germans have significantly more range, and is marginally faster on the highway. The US tank has one more machine gun. They are both modern variants of designs that are the same age.
Except for the difference in engine philosophy, they are pretty much an even match and the crew would make the difference if they went head to head.
But I'd never underestimate German armor.
I think fire control is really the deciding factor today. The Abrams can fire at moving targets while it is also moving at top speeds. I’m not sure what the fire capabilities are on a Leopard or a British Challenger.