How about the Spitfire Mk XIV
Speed - 448 mph
Ceiling - 44,500 ft
Rate of Climb - 5,110 ft/min
Armament - Two 20mm cannon and either four .303 MGs or two .50 MGs
If you compare the performance of the P-51D and Spitfire XIV, the Spitfire comes out ahead in speed, rate of climb, ceiling, turning circle, and handling; the P-51D has the edge only in range and rate of roll.
While many P-51D pilots certainly would defend their aircraft over any other, many who either flew or fought both have stated quite clearly that they think the Spitfire was a better fighter:
Some quotes:
William Dunn (US fighter ace who flew Spitfires, P-51s, Hurricanes, and P-47s): "Now, if I had to make the choice of one fighter aircraft above all the others - one that I'd rather have tied to the seat of my pants in any tactical situation - it would be, without any doubt, the world's greatest propeller driven flying machine - the magnificent and immortal Spitfire."
Eric Brown (RN test pilot and holder of the world record for number of types of aircraft flown): "I have flown both for many hours, and would choose the Spitfire [over the Mustang] if given a choice in a fight to the death."
Writer Jerry Scutts, quoting German pilots in his book "JG 54": "The Jagflieger had to keep a wary eye out for enemy fighters, particularly Spitfires, a type JG 54's pilots had developed a particular aversion to...Pilot reflections do not, surprisingly enough, reflect over-much respect for the Mustang or Lightning, both of which the Germans reckoned their Fockes were equal to - unless they were met in substantial numbers."
Gordon Levitt, Israeli fighter pilot, comparing the Spitfire, Mustang, and Avia S-199 (Jumo-engined Bf 109), all of which the Israelis flew: "Despite the pros and cons, the Spitfire was everyone's first choice."
Karl Stein, Luftwaffe Fw 190 pilot (who served mainly on the Eastern front: "English and American aircraft appeared on the scene in those closing days of the European war. Spitfires were the most feared, then Mustangs..."
USAAF 31st FG War Diary (when transferring from Spitfires to P-51s): "Although pilots think that the P-51 is the best American fighter, they think the Spitfire VIII is the best fighter in the air."
USAAF pilot Charles McCorkle (who flew both in combat), reporting on a mock combat between a Spitfire and Mustang in 1944: "Now we could see which was the better aircraft...a Mustang and a Spit took off for a scheduled 'combat', flown by two top young flight commanders. When the fighters returned, the pilots had to agree that the Spitfire had won the joust. The Spit could easily outclimb, outaccelerate, and outmaneuver its opponent..."