When the Shield came out, a friend lucked into finding one in stock. He let me borrow and shoot it for a couple weeks. I was sold and bought the first one I could find, which took a while. I looked for a few weeks before finding one in stock anywhere, rushed there and bought it. Shields were HOT when new and it was HARD finding any stores that had them in stock. When they came in, they sold out FAST!
I had been carrying an ancient Glock 26 before that, Never an issue with the G26, it was just kinda bulky and chunky. The Shield is enough thinner that, for me, it hides a lot better under just a t-shirt during the summer than the G26.
I really love my Shield. I lost count a long time ago of how many rounds I have put through it, but it is several thousand. The only issue I ever had with it is the magazine release rusting one time after I sweated on it like a pig one summer day working outside. It still worked, it was just hard to press. Not a big deal, simply pop it out of the frame, clean it up, smear some BreakFree on it and reinstall. Every time I clean it, I dribble some lube on it and work the release several times to get the lube down inside the frame, wipe off the excess and never another issue.
I know it's a minor consideration, but the finish is incredibly durable. I have been carrying my Shield pretty much daily for several years in an Alien Gear hybrid holster and the finish still looks like new. I know the slide is melonited stainless and rust and corrosion really aren't a problem, but I really like that the finish has held up so well over the years.
I will freely admit that I have never tried a Sig P365, a Walther PPS or any of the other really small CCW guns. I will say, however, that they would have to be substantially better than my Shield to make me replace it. For me, it is perfectly sized (I can get about 3/4 of my pinky on the grip with the 7 rd mag installed, so absolutely no wasted size on the grip), wonderfully accurate and recoil is perfectly controllable. It truly is a small gun that shoots like a big gun and I can't see anything replacing it for me.