Best-sounding aircraft
I grew up very near an AF base and not far from our large municipal airport, so I got to hear plenty of great-sounding aircraft.
I'd say nearly any multi-engine radial. I heard plenty of C-47s. Also heard RC-121s and C-54s (I think - could have been C-118s). Also heard and saw others, such as C-119s. Then, when I was a college student, I traveled through ORD quite a bit. I remember sitting in a 727 waiting for takeoff when a C-124 Globemaster took off. I could hear the roar of its four radials inside the 727!
Last summer a beautiful natural aluminum B-17 spent a few days here. I saw it while running an errand for work downtown and then as it flew over my house. No mistaking its radials!
Then, when I was living in OKC, someone brought in a P-51. There was something particularly exciting about that Merlin!
I agree with the above about the sound a 1900 makes when you throw it into beta. That's cool, too.