Jan Libourel of G&A loved the phrase "wonder nine" and used it extensively, almost ad nauseam.
Mass LEO acceptance of the 9mm, largely because of convenience and perceived extra firepower that the high magazine capacities of the Beretta 92SB/Sig P226/ Glock 17 gave, began the true stampede from wheel guns to semi's by the early to mid eighties. Everyone was amazed at that time that you could get 15+1 (17+1 for glock) in a gun versus the six shooter or the 7 rounds in a 1911A1, hence the "wonder".
Note that by 1986, the "Miami Shootout" is attributed for pushing the FBI to fully adopt autoloaders as standard, and to eventually "up gun" to the 10mm (and then finally the 40 S&W) as they felt the 9mm had lost some of its wonder.
Having owned 9mm, 40 S&W, and .45's at one time or other, I still like the 9mm best for what I do with it: plinking, target shooting and general fun. To each their own, however.
Had the opportunity to shoot all the nines around (except the P7, Walther P88 & P99 and Steyr, strangely) and each is unique. I do have a real soft spot for the big old Beretta, though. The Sig was the most accurate I had ever owned. But the Glock was the quickest and easiest to use, just keep your finger off the trigger, where its supposed to. Everything else was really cool in its own way but just ok. That's only IMHO

YMMV!