Merlins are kind of harsh compared to the P-38
I've watched countless Mustangs, several Spitfires, a Hurricane, and the Battle of Britain Memorial Flight's Lancaster. They're all great planes and the Merlin was a fantastic engine that made truly historic contributions to winning the war. I wish I'd get to watch a Mosquito but I don't know of any airworthy ones left. Kermit Weeks has a Mosquito (last seen by me at Oshkosh 96) but it was on static display.
The twin Allisons on a P-38 have a very smooth, sexy sound. I think that's due to the engines having turbochargers. Merlins are supercharged with very short exhaust pipes, so they sound harsh by comparison. Still, I wouldn't throw rocks at anyone who offered me a ride in a Merlin powered plane.