Number wise (if we asume engineer estimate of XP-72 is correct), then it is the one with highest rate of climb. Even higher than XP-51G
Spiteful: 4890 ft/min (24.8 m/s) at 2000 ft. No additional information
XP-72 with twin props: 5250 ft/min (26.67 m/s) at sea level, take 3.8 min to climb to 20,000 ft
P-51H: 5120 ft/min (26 m/s) at sea level, take 4.58 min to climb to 20,000 ft
XP-51G: take 3.58 min to climb to 20,000 ft
F4U-5: 4840 ft/min (24.58 m/s) at sea level, take 4.7 min to climb to 20,000 ft