New here, but I've owned both weapons in question, so thought I'd chime in.
Both are terrific handguns IMO. If you thought the Glock was a little thick, the Beretta may be too large to handle comfortably. The grip is very thick compared with most other autoloaders. I ended up selling mine because of this. I went with the Glock as I intend to compete and parts and accessories are plentiful and inexpensive. Otherwise, I really thought it was an ugly gun. I preferred steel, exposed hammers, and wood stocks on a handgun. Now, after shooting it extensively the last 6 months, I absolutely LOVE the Glock. Here are just a few observations of each handgun:
Beretta 92:
Nice appearance
Accurate
Reliable (in my experience)
Large grip may be better suited for someone with large hands (a thinner grip is available from an aftermarket vendor that I don't recall at the moment)
SA trigger easier to shoot accurately, smooth DA when necessary
Limited sight options due to front sight integral with frame
Safety/Decocker on slide can be difficult to reach in firing position
Mine was very loud (due to open slide design)
Generally more expensive than the Glock
Requires more frequent cleaning/oiling to function properly
Glock 17:
Ugly! (IMO)
Accurate
Extremely reliable
Abundance of available accessories/modifications
DA trigger more difficult to master than SA mode on Beretta (but still OK, and numerous trigger modifications are available)
No external safety (negative or positive depending on your viewpoint)
Functions even when dirty, requires little lubrication
Much easier to carry in a concealed fashion (IMO)
Stock sights suck, but numerous aftermarket options are available
I really felt the Glock didn't have much "character", and I wasn't really excited to purchase one. I just felt it was the best option for me to begin practical shooting competition with. I didn't like that it didn't have an external safety, but I quickly became comfortable with this. I really didn't like polymer, striker-fired guns at all, but the Glock has made me a convert. Between these 2 options, I come down solidly on the side of the Glock. However, if Glock is on your list, I'd highly recommend you also check out the Smith & Wesson M&P and Springfield XDm. I enjoyed shooting each of these more than the Glock, but again went the Glock route due to availability of parts and accessories. Hope some of this information helps.