Re: AR-15 use stock sight,or red dot???
I have both on my AR. Once my red dot is sighted in, it's almost too easy hitting the bullseye every time. One thing to consider is the size of the actual dot. The bigger dots are handier for getting on a target that is closer, say 25-50 yards. Mine is a one MOA dot, (very small), so it is more accurate at longer ranges, but in an up close self defense type scenario, I would prefer a bigger dot.
I also have a fold down type back-up iron sight (BUIS)mounted on the rail. I like using it at ranges of 100 yards and over. Also, when the battery dies on the red dot at some inopportune moment, you can just flip up the BUIS and keep firing. So I recommend both.
If your AR does not have a removable handle, you can buy a mount for the red dot to go on top of the handle. Bad thing is that you have to raise your head up a good deal to use that way. Just doesn't feel natural to me.