There is little doubt that the P-51 and the F4-U Corsair were the two big game changers in fighter craft in WWII. Having had the privilege of knowing veteran pilots of both, the description of either being "easy to fly" might be a little stretch. The one vet until a decade or two back, owned and still flew both. He adored his Corsair, but always kept a wary eye on the Mustang. He said either could bite, but the Mustang could bite you faster and harder.
My personal vote as favorite would go to the Corsair, mostly as aesthetic preference. But the concept of saddling up behind the enormous torque of either of these is something all pilots crave in their dreams.
Those old pilots, just kids in the day, did have to live by a couple basic rules which the Mustang pilot recounted to be "No Smoking Within 24 Hours, and No Drinking Within 50 Feet of the Airplane".