The Ford vs Chevy thing has been going on for a long time. The P-51 also has a rival, the P-47 Thunderbolt. Although very different designs, they were used for similar operations. Each aircraft soon found a niche that it would excel in.
Both Mustangs had very effecient assembly lines, making the most of precious time. Ford was fighting a war of marketing and sales, while North American Aviation was fighting World War II. Both circumstances produced creativity and first of its kind designs with dedicated design teams.
The final is say is easy: Two classics, etched in history.