On almost all forums regarding the warbirds, as the most modern fighter planes, peoples are very impassioned about that question.
But very few are those who were able to compare effectively - i.e. in flight - the different aircrafts they are discussing about.
Handling vs Maneuverability
First, I want to rule out a wrong question.
When I was learning to fly, I was used with the very light ailerons of "my" first plane (a Morane-Saulnier Rallye 880 B 105 hp).
So, transferred to the much faster Robin DR 400 - 140 hp, the ailerons were not so light and I thought the Robin as less nimble than the Morane.
Some dozens of flying hours later, I cannot feel significant difference of maneuverability between the 2 aircrafts.
British test pilots seemed to have separated the handling capacities of an aircraft from its maneuverability.
Nevertheless, reading the excellent British reports regarding the Messerschmitt Bf 109 E (http://www.spitfireperformance.com/spit1vrs109e.html), you can read that above a given speed, the ailerons of this fighter were becoming "solid" or "immovable".
So these 2 characteristics cannot be seen as independent at all.
Habits and skill
A forgotten fact is the pilots of different countries learn to fly on different school planes which don't share all the same properties.
So, once becoming operational fighter pilots, they prefer some maneuver that are not seen as natural for pilots belonging to other countries.
In France during the 30's, the school-planes were the Morane 230 high parasol wing monoplane or the Hanriot 436 single bay biplane.
The following step used of Nieuport 62 sesquiplane, vilified by the French CEMA (official test flight center) because her landing characteristics were very sharp and also because she was directly derived from the Nieuport 42.
This last fighter, during her first full speed diving tests, had triggered the first ever recorded manifestation of the aileron flutter, resulting in a fatal crash.
The efficiently modified Nieuport 62 was much more stable and easy to fly in aerobatic (as it was said by Roger Sauvage - who was trained on this aircraft - a French ace who obtained the last 15 of his 16 victories against the Luftwaffe within the Normandie-Niemen regiment).
This fighter was used during the first year of the Spain War by both sides, and also - shortly - by French pilots in Numidia - oh, excuse-me: in French North Africa - at the beginning of the second World War.
Another reminder consist in the very interaction between any kind of vehicles (including horses...) and their pilots. In the cases of horses, it's a plenty accepted - and well known - relationship.
In a mechanical vehicle, the pilot must also feel a full harmony with the dynamic characteristics of his vehicle. Such a relationship may be based on the relevance of the training.
If you have some doubt about that, remember (!) how vilified was the Bell P39 Airacobra by American and West pilots and how the Soviet ones liked her.
Really, what could have been the feeling of an American pilot if he had to fly the quite unstable and diminutive fighter Polikarpov I 16 ?
Moreover, the assessment of a fighter is never the same following the date of the flight trial was done.
In 1939, the test pilot Michel Détroyat - former chief pilot of Morane-Saunier - after his flight test on the D.520, said the Dewoitine fighter was extremely maneuverable.
The Belgian test pilot, Major Arendt, who might have flown the British Hurricane I fighter, flew the D.520.
After he had sent his report, the Belgian government decided to buy the license of the French fighter.
One year later, the French operational fighter pilots feel that their new fighter was very nimble. The actual Capt. R. Clausse (Grp. II/3) in the foreword of the book of R. Danel, Le Dewoitine 520 (Docavia #4) - the Bible on this fighter- wrote:
"A show plane? certainly not. But an uncommon fighter, outstandingly maneuverable, as fast as any other fighter (in May 1940, of course), with an excellent rate of climb until a high ceiling, diving at fantastic speeds, fitted with an efficient armament, excellent gun platform..."
Capt. J. Pape (Grp. I/3) told us:
"The handling trials allowed us to see this fighter as very maneuverable, easy to fly.
The pilot training being without problem, we thought we might be already operational.
However, it appeared the plane needed more than 100 modifications! Indeed, the design of the aircraft was good and she had good characteristics and, after finalization, she was really excellent. Unfortunately, she was not truly experimented in time".
These last words regarded the people who had imposed the Hispano 12 Y 45 in place of the HS 12 Y 29.
After November 1942 and up to mid-1944, Germans had ordered new Dewoitine 520 for using them as advanced trainer.
It's a proof they feel this fighter as easy to fly and very easy in aerobatics.
The German ace Ernst Schröder was trained on the French fighter.
He did not like her ground behavior as also the frequent sabotages made by the French worker of the Toulouse plant (the present Airbus plant). However, he said:
" What a delightful plane! Very light actions on the commands were sufficient to do all the aerobatics. A loop needed only two fingers. Not any German fighter at that time was able to offer such a fineness of flying...."
Italian pilots used the Dewoitine fighter after mid-April 1943, to struggle against daylight American bomber.
The reason was the Italian designed fighters lacked of a powerful weapon.
The D.520 had a deadly Hispano HS 404 20 mm gun with unfortunately (for them) only 60 ammunition.
The engine was the same as fitted in late 1939, so the fighter appeared pretty slow.
Obviously, the Frenches never warned Italian pilots with the fact that it was forbidden to combat when the wing tanks were full of fuel: They must be used only during ferry flight, otherwise the fuel would go to and fro, altering significantly the handling properties.
So, most of the Italian pilots disliked the Dewoitine 520.
There were notable exceptions, as the pilots of night fighting and, also, the great ace Luigi Gorini, who, in an interview, explained that the difference between a Fiat CR42 and a D520 was as great as the one existing between a tricycle and a Ferrari!
In another text, he told: "tested at her minimal speed, the fighter was perfect and extremely maneuverable, as he had seen it while he was fighting over the Cannet des Maures, the June 15, 1940."
(the combat of the June 15 allowed to Pierre Le Gloan to down successively four CR42 and one Fiat BR20 in a 50' flight).
The controversy staying, another post will explain a bit more.