I got hooked into plastic modeling of WW2 acft when I read "The Hurricane Story" (until @9 yrs old, I primarily read midieval stories) and also took particular interest in their characteristics and whatever facts I could glean from WW2 veterans who knew anything about them.
As each of these responses indicates, everyone has their own opinion, including the veterans that flew them. Obviously, each acft is better for certain operations than for others. It may be neat to think about a dogfight between a B-17 and a Heinkel 111 but in reality it would probably be quite boring to an observer. My point is that the P-38 and, especially, the P-47 hit the scene in large numbers sooner than the P-51, were fast for their time but not as manouverable in a dogfight as were many contemporaries -- if they got their guns on you, however

-- yet this was true for most! The P-47, in particular, was very durable and could carry a substantial payload; although the P-51 (or even a Spitfire) could definately do the job, I'd agree with many that the P-47 was the better choice for a ground attack -- but I'd certainly vie for the P-51, Spitfire or even a Hurricane (a bit slower but very manueverable) for a tight-in dogfight.
Then you have the fact that many designs would have been more proficient had a better power plant -- or other factors -- been applied to them (the first P-51s did not perform so well with the Allison engine). For some, looks seem more important than performance: good and bad are not necessarily stand alone adjectives when both looks and performance are considered.
My overall opinion is that, when it comes to flight, any operable plane is much better than flapping your arms real fast at 3000 feet without one

.