Depends on what you mean by WIDELY USED. Total number or total "units" using them? And currently used, or over a long period of time?
If you're talking about WHAT'S currently used...
CZ's claim that its most widely used, includes lots of small police and military units but relatively small total numbers. I'm a big CZ enthusiast, but I think I know marketing HYPE when I see it. Bogus. Great guns, however. (Relatively few military units use CZ, and Turkey now uses their own "clones".)
Ditto the claim about Browning High Powers. At one time (WWII) they were relatively widely used, but most countries have long since phased them out. SA guns are not loved by most militaries or police units.
There are probably more Beretta 92s in use than anything else (except, perhaps in the Chinese military). The US's use of the 92 probably jacks the numbers up significantly. Then there's the Glock 17 and the SIG 226 (and maybe the 228).
Found the following link on the web. Rather than steal this stuff (unintentionally), I'll just post the links. It is several years old but I doubt that things have changed much since it was compiled. You'll see lots of Glocks and SIGs listed.
www.fortunecity.com/tattooine/leiber/50/DGAAA.html
Scroll down to part 4 - Special Interest Issues.
You find listings for various police and military units.