The .45 is a really fun round to suppress. It stays subsonic so all you really hear is some action noise from the pistol then a very satisfying thud when the heavy bullet hits the target. 9mm is great when you have work to do like concealed carry or training but for pure shits and giggles I love my .45.
I'm ambivalent but lots of rounds stay subsonic. 147gr 9mm for instance.