Historically: Luger.
The original wondernine: BHP
The modern wondernine: Beretta 92 (as seen on TV! How could Bruce and Mel both be wrong?)
The most bullets in a 9: Glock 17 with +2 extension (sure, there are hi-cap Caspians, but that wouldn't seem right.) Plus, is invisible to X-rays and metal detectors.
Most perfect man/machine/caliber oneness ever: P7M8 or M13
Yeah, the P7M13 has the bells AND the whistles. Oh, baby.
It all depends on whether you view 9mm as an ancient military workhorse, or the ultra modern caliber-for-all-seasons.