Warning, massive wall of text:
I have both a Cougar 8045 and a G21. I shoot both fine, and between the two, I have about 20,000 rounds through them. I have never had a ftf, fte, light strike, anything, on either one. I keep them in good condition though. They shoot everything I have put though them, and the accuracy is comparable. I shoot about the same size groups with each at the same distances with the same ammo.
The Cougar has a little bit different feel to the recoil based on the rotating barrel. The recoil doesn't pull as high, but you can feel the rotational force on it, especially shooting +p rounds in it. If the hammer is down, it is a long trigger pull on the first round, after that, it is much crisper and shorter. Biggest downside is the frame width if you get ambi safeties on it (1/4 wider than the Glock). I also had a hard time finding a concealed holster that fit me and the gun. Mine doesn't have a round indicator for the chamber, but you can actually see a tiny bit of daylight through the barrel to the left side of the hammer if there isn't a round chambered. Very noticeable in daylight when you come up to target. Hammer also has a halfcock safety, and decocks.
The Glock is narrower at 1&1/8" but is 1/2" longer. Weight wise, fully loaded, it weighs about the same as the Cougar but is 13 rounds vs. 8. That is picking up both guns and feeling for a difference, I didn't put them on a scale or anything. That is also with the light on the Glock. I did get a ruler out and measured the slide widths just now
Both have nice sized grips if you have average sized hands. I hold in something that I can only describe as a Weaver or Modified Weaver grip and I get good engagement of both hands. My wife thinks they are both a bit large, but she has no problems shooting either. She prefers the Beretta, and even though she doesn't shoot as often as she should, she shoots about a 4-5" group at 7 yards with both. Before surgery, I was shooting about 2" groups at 7 yards. Some better, some worse. Even after several hundred rounds, I have never noticed a significant change in point of impact with either gun out to 25 yards. (That's the farthest I normally practice with handguns at. I have made 100 yard shots with the Glock for giggles. Best shot was 1" off bullseye on a full sized silhouette. Lol, and yes, I had a witness. He was using a spotting scope for me.) Most of my friends that have shot them found them easy to shoot and put pretty good groups down. Except the guy that was spotting for me above... he can't shoot handguns worth a darn, he pulls something terrible, and I never could break him of it.
I like the fact that the G21sf has the lower rail mount. I keep a 300 lumen switch activated light on it, and that's the one that sleeps by the bed. I did not like the difficulty of trying to swap out the rear sights on the Beretta. Without a press, I don't think you can do it. I bent two brass rods trying to get mine out to put a Burris Fastfire on it. I gave up. (If you check the advertisement pictures for the Fastfire II, it shows a Cougar 8045 (you can even read the model number on the slide in the picture)). Both will fire without a magazine. Both are easy to field strip and clean. However, the rotational action on the Beretta has more wear points and I think in the long run, that will limit the life of the gun before I have to start looking to replace parts, though I think I am good distance away from that. Oh, and the lower rear corners of the slide on the Beretta are VERY sharp points. I actually cut the web between my thumb and index finger once while pulling the slide back to field strip it. Even with about 4,000 ish more rounds through the Glock, there is less wear on the barrel.
I don't have experience with the other three, but I have a lot of experience with those two. Either one should do well if you chose to go with them. I have been quite pleased overall with both. I'm assuming that even if you are looking at a Stoeger Cougar, it should be made off the same molds as the Beretta, and I would assume (yeah, yeah, I know, you and me) that they perform similarly.
Hope that helps. And if not... NC isn't that far. Maybe we could meet up one day and you can try em both, though the odds of that are probably pretty low.