That's easy... (I assume we are restricting this to props right?)
I'd take an F8F Bearcat, which is largely based on the FW-190A series (basically a 190A-Hellcat hybrid) but with the much better US P&W 2800 C series engine. Add in NO2 injection from the 109K/Ta152, and arm it with 6 x B20 cannon from the LA7-FNV with 200 rpg (these were not the most potent cannon, but they were quite light so 6 could easily be fitted).
The result would be a 475 mph class fighter that could climb at nearly 7,000 feet per minute, turn on a dime, had excellent durability, and spit out 80 rounds per second of 20mm. And it could operate off a carrier deck too!
PS: F4U was tougher than the P-47 (USAAF determination after post-war testing)
PPS: The quick change engine on the F4U and F6F probably made these easier to maintain than the Hurc. It only took a few hours to swap out an engine.
PPPS: I don't think any liquid cooled engine is a contender... air cooled engines were just so much more rugged. One hit to the radiator of a liquid cooled plane and it's done in 5 minutes. But a radial could have a cylinder or two blown off and still make it hundreds of miles back to base.