It's ALL pure PREFERENCE.
The key to accurately shooting a handgun is in the handle or how you hold it... Some people, such as myself, have smaller hands... I like it for the following reasons:
1.) Single Stack Frame - Slim, sleek, sexy, but most importantly ===> COMFORTABLE, and BEFITTING! Beretta, Glock, and HK USP & MK Series, ANY double stack does not fit well with me, and we all know FIT is the most important thing to look for. 1911A1 fits all hands!
2.) Safety - 1911A1's have TWO active safeties, compared to the Beretta's ONE. Not only is this good, but the thumb safety is in a FAR better place than that of the Beretta. PERIOD. The Beretta's safety is a pain in the ass! The 1911 has options for extended safety which puts it in prefect reach. This sort of fits in with the "Feel" of reason #1.
3.) Slide Release - 1911A1's can have (and often do) extended slide releases, that way smaller hands don't have to "CANT" the frame in their hand to release the slide, making reloads infinitely faster.
4.) Parts Availability - The 1911A1 has been around for so long that there is a HUGE market for them, and replacement parts are dirt-cheap.
5.) Power - I don't care about velocity, expansion, ft/lb energy levels, etc... It's just proven that the .45 ACP can stop humans (and some animals) almost immediately, 9mm sometimes isn't as effective...
6.) Cost - For a 9mm Beretta in a single stack configuration, I could buy 2 RRA 1911A1 pistols for that much, or buy a great Kimber Custom Classic Stainless .45 for that price. Plus you'd STILL have to deal with the ergonomically F*cket Up safety. I'd rather take the Kimber any day.
7.) Ammo - Surplus ammo costs about the same as the 9mm in certain cases (based upon sportsmansguide prices), and you literally get "More BANG for your buck".
Sh!t, I could go on & on all day about this. I just wish they made a 1911A1 in 9mm that was RELIABLE, springfiels & others just aren't as reliable as the .45 ACP versions. I think a .40 Kimber would be great, but I'd never shot one, so I'll not trust a gun I haven't shot yet...
-iNuhBaDNayburhood