I would recomend that anyone getting their first handgun purchase a good revolver. IMO, NOTHING teaches you a better trigger stroke than learning how to shoot a revolver in double action well. I may shoot a bit tighter and faster with my semi's but feel the reason for that is because I warm up with a revolver at every range session.
If that interests you, my personal recomendation would be a 4 inch model 686 or 620. They are well balanced with enough mass to permit shooting full power 357 Magnums to be enjoyable provided you chose a grip that fits you well. BTW, I found that standard grip to be too small and replaced it with the larger monogrip for the 500 Magnum.
If you want a semi auto, I would recomend that you purchase the Glock, the S&W Sigma series has a reputation for a horrible trigger. The S&W M&P series is a great semi but priced a good 200 dollars or more than the Glock your looking at.
BTW, per your last post I strongly suspect the 6 inch 357 you shot was a 686. I would recomend that you choose the 4 inch version as a first handgun for one very simple reason, the swing weight of the longer barrel will impede your shooting in rapid fire drills. I just purchased a 6 1/2 inch 610 and am currently struggling a bit with that long barrel. While there is less muzzle rise, when I bring the gun back on target, the added inertia causes me to swing past the target when trying for a fast repeat. As a consequence, I either have to slow down or except a larger grouping. Currently I can empty my 4 inch 620 into a 4 inch group at 30 feet with a 1/2 second interval. With my 610, if I try to hit that interval time, my groupings are around 7 inches at the same distance. Of course the upside of having to muscle that long barrel is that any improvement with that gun will carry over to my shorter barreled handguns but I still wouldn't recomend it as a first choice.