I'll take the P51B please
I know the P51 is considered the better aircraft but give me a MK9 Spit anyday 
Oh yes?
I didn't see that on the list of options
I base my opinions on my dad's assertions, he was posted temporarily to the Poles when they had P51As. He was an "Armaments Technician" assigned to teach their armourers the intimate intricacies of the interrupter gear. Seems the Air Ministry thought it a good idea to stop their cheery pilots shooting the props off their Allisons in fits of boyish enthusiasm.
He always swore that ditching the Allison and the associated nose mounted guns in favour of the Merlin made the Mustang a fine aeroplane, as noted since by hundreds of people
Yes the Spit MkIX was wonderful, but on balance, being able to dogfight halfway across Germany even to Berlin, gives the 'Stang a little edge I suppose, even though the Spit remains my fave beastie.
My dad had been an Armourer at Hawkinge in 1940 and served as such in various Fighter and Bomber units 'til late in the war when he became an Airgunner in Coastal Command.
Sorta gave me a boyish respect for his opinions...