I have several Sidearmors and like them, but I don't have that much experience with other Kydex holsters. My Sidearmor IWB is very comfortable. It's very slightly thicker than some others I've seen, but we're talking tiny, tiny differences. The IWBs can be readily switched from belt loops to J-hooks, which is nice.
One feature I really like on the IWB is that it rises next to your body to the same height as the grip and slide. This keeps the grip and slide from touching you, and more importantly gives you a very easy way to guide the pistol into the holster, which makes it easy to reholster without looking. For my money, that's an important feature. It also clicks in, so you know it's secure.
I don't know why the poster above doesn't like the way loops are attached, but I'd like to hear more about it.