1. Tiger Moth – it taught so many to fly during WWII and brought private flying to so many after the war.
2. Hurricane – as other posts above: it did more than any other aircraft to hold back the Germans in 1940 and marked the transition from biplane to monoplane.
3. Mosquito – one of the first and most successful multi-role combat aircraft setting the pattern for combat aircraft right up to the modern day.
4. Comet – ushered in the age of commercial jet travel.
5. Tornado – has been the backbone of the RAF’s combat capability for more than a quarter of a century.