I always did think the p-51 was the best wwii aircraft in the world, is it? And the spitfire is my favorite, but i'm still going for the p-51.
It was in Europe,if you needed to fly a long way and have a decent fighter. If you got involved in a turning fight with either of the other two you would probably be glad of a parachute! All three machines had strengths and weaknesses.
It's horses for courses.
Timewise it's fair to compare them. They are all 1930s,pre war,designs,The P-51 is only three years younger than the Spitfire.
If I was going into a dogfight I'd take the Spitfire. If I took my Spitfire on an escort mission I'd run out of fuel before I got to the fight! I'd be happy to take on a P-51 in a Bf109........you can see what's happening here.
Cheers
Steve