Lots of good choices. Impossible to pick only one.
WWII
Brit: Mosquito
US: P-38 ( actually got to put my hands on a real one. Didn't wash my hands for a week!) F4U real, real close second
Jap: J7W
German: Do 335
Ital: 2002
USSR: Mig-3
Korean Era
US: USN Panther
USSR: Mig-17
Vietnam Era
US: A-4, SR-71
USSR: Mig-21 (like anything delta shaped)
Current
US: F-14 mature beauty
USSR: Su-35
Euro: Tornado
Honorables: B-58, XB-70, XB-38, Il-2m3, Spit, 109, 190, A6M, 262, P-51, to a downed airman PBY, B-17, Typhoon, Tempest, ....
Oh, I give up on keeping the list down to less than 100. And I haven't even started on the civilians....