I'm probably not as well qualified to answer as the previous posters, because I actually own both the Glock 34 AND the Beretta 92 FS.
The FIRST and OBVIOUS answer is, GET THE ONE THAT BEST FITS YOUR HANDS.
I assume you already rented or borrowed both, so you have (or certainly should have) figured out which fits you better.
The OBVIOUS 2nd answer is that you might want to buy both - since both are excellent and you really can't go wrong with either.
NOW, for folks who may be considering the same choice, I"ll add one more comment. When you borrow or rent these weapons, make sure you shoot at least 100 rounds through each and DON'T stand there swapping back and forth from one to the other. The trigger pulls are completely different, and if you haven't shot Glocks much, it takes about 50 -75 rounds to get used to the longer "double action" feel of the Glock trigger. Once you get used to them, they shoot great.
Having said all of the foregoing, my Beretta sits in the gun safe most of the time (haven't shot it in about a year). The Glock 34 goes to the range at least once a week, and sometimes more often.
The CONSISTENT Glock trigger pull (first shot same as all subsequent shots) is, for ME, the tie-breaker. I can shoot both guns pretty well, but it takes a tremendous amount of work to learn to hit well with the Beretta in double action AND in single action mode. The Beretta double action mode is much stiffer than the Glock, causing most folks to lose a lot of accuracy on the first shot. THEN, the second shot has such a comparatively easy trigger pull, I always have to guard against an AD on the 2nd or 3rd round.
Nevertheless, I won't ever get rid of my Beretta - it's a great weapon. In my case, the Glocks just serve ME better. Especially since I own a number of handguns in different calibers. Eight of them are Glocks (in 9mm, .40 and .45). They all have the same trigger pull, whether it's the first round or the 17th (in the G34). So no matter which one I (or my wife) pick up, we are equally accurate with any of them.
Just remember my first OBVIOUS answer - the one that fits you best, and thus shoots best for you, is your best choice.
AND, whichever one you picked, practice with it as much as you can.
Stay safe,
Dawg23