Hard to pick just one but I would say Bomber - Avro Lancaster Fighter - P51D Mustang Multi Role - De Havilland Mosquito If I had to narrow it down to one, it would have to be the Mosquito. It could, and did do anything.
I thought I would ask Grandson #2, aged 8 and a regular at Duxford. He mulled for a moment and said: "Boeing Stearman or North American T6 Texan/Harvard." I was glad for the additional detail on the latter, as a 'T6 Texan' by itself would have thrown me. When asked to make a choice, he picked the Harvard, telling me almost immediately that it was the RAF's longest serving WW2 aeroplane. This was not the model I was expecting him to choose (PBY Catalina) and I was unaware of the additional detail, but ......... an interesting choice. I might have gone for the DH.103 Hornet, possibly swayed by Winkle Brown's opinion of them, but although the first prototype flew in 1944, it is on the cusp of the question at hand so would go for the Beaufighter - 'Whispering Death', or not.