They could have picked the P-47, the P-51, the F6F, the F8F (too few made really) the P-38, or the F4U.
The P-47's were pretty tired from a LOT of sorties in WWII. The P-51 stayed on for awhile, but was intended for higher altitude work mostly. The F8F was probably right in there as one of the best performers ... but the end of the war saw the end of the orders and they didn't make many ... so it's pretty much out. The P-38 wasn't really a first class fighter-bomber ... it was a pretty good fighter, but not a great bomber.
That leave the F6F and the F4U.
We KNOW they picked the F4U but nobody in here knows why the F4U was picked ... unless they were in on the decision. If so, please chime in here. I certainly wasn't. I think the Hellcat would have been a better choice for ease of maintenance, toughness, far better manners at slow speeds (much nicer around a carrier or getting into or out of a short strip, better controlability right at liftoff) and in bad weather, decent bomb truck if not quite as good as the Corsair, and better visibility over the nose. Great accuracy in practice and in the war.
We KNOW they chose the hose- nose. I just wish I knew why ... speed wasn't an issue since jets were obviously on the way. 20 - 40 mph was nothing when carrying bombs ... the jets were 150+ mph faster. The Hellcat could turn tighter but the Corsair rolled better. Climb rate about a wash with equivalent engines and, if they HAD decided on the Hellcat, I'm pretty sure a more powerful R-2800 and a 4-blade prop would have shortly been in the works, possibly even as a field retrofit with a QEC package.
In the real world, the Corsair did pretty good work so it's hard to argue they made the wrong choice, but it is also hard to say the F6F would not have done as well given its many advantages. Another "what if" that can be sidestepped by just saying that the Corsair was picked and did OK in the early jet era when called upon to deliver the goods.
Go Hose Nose. Sorry faithful Hellcat ... but you got aced out after the war.