I am a fan of about anything that flies but there are a few that when I see them, I have to stop, listen, and watch. I have a thing for the sounds they make. Pretty much like anything that takes to the air but a few that stand out to me.
P-51 I'd give my left nut for a 30 min flight.
B-52 Big hurt that just sounds vicious.
C-47/DC-3 Love those big radials. Get to see them often heading out to the bush doing cargo runs up here.
C-5 The big GE turbofans can't be mistaken for anything else.
UH-1 Huey Who doesn't like the sound of one?
F-22 Much maligned but still a very impressive aircraft that I get to watch fly nearly daily now that the F-15s have been reassigned. Their turbines make a howl that gives me goosebumps.
A-10 If I had been a pilot I would have loved to fly a flying tank.
SR-71 Never got to see one in flight but was an airframe that is still ahead of the times.