My vote would go to either the P-39, P-40, or P-51/51A: any non-turbo Allison with short stacks. The P-38 was too quiet. Water cooled V-12 with long exuast pipes running to the turbo. The props made more noise than the engines did! Merlins had a nice sound too, but not as smooth as the Allison. R-2800 is an earful. Particularly in the P-47, with the turbo whine. Never got a chance to hear the DB in the 109. What did they sound like?