There are about a dozen or so different designs from different manufacturers of Optic Sight Mounts for Glock Pistols, but I decided on the Aimtech APM-1 Mount as my preferred one for a number of reasons. The first and main reason is that it is a STATIC mount, meaning it is independent of the movement of the slide. The previous mount I used for my Burris Fast Fire 3 was a Slide Mount, but over time I discovered some issues with that type of mount after firing a couple of hundred rounds in full auto with it. I plan to discuss this more in detail at a future date somewhere in my blog, but suffice to say for now I decided to use one that would not require the FF3 to be mounted on top of the slide itself.
The second reason is the fact that it leaves the Glock's frame rails free for use with other accessories. Most Glock Optic Mount designs use the frame rails to anchor on to, but I use Vertical Front Grips (VFGs) on my Glock, hence I wanted that rail free. Some mounts that use the rail also allow VFGs to be mounted on them, but I found these to be ineffective (again, further discussion on my blog at a future date). The APM-1 uses the Trigger Pin and Trigger Housing Pin to anchor on to, leaving the rails free for use.
The third reason is that it anchors itself to two points (as mentioned earlier), making for a much more secure attachment. Be careful of using mounts that secure itself to only one point (i.e., like those using the Frame Rails only) as they are less secure and will likely tend to move around during actual firing and/or handling. Here is a close look at the mounting pins as they are attached to the frame.
