The first thing you will notice when you hold a Glock is the grip angle.

Try this, eyes open, look at your target, then close your eyes, draw your unloaded pistol and aim to where your target was. Open your eyes. Where are you pointing?

Going from an HK, S&W, or a Springfield XD and moving to a Glock you will likely find that you are pointing pretty high. The Glock's grip angle is more obtuse than the standard angle of an HK, XD, or S&W.

It makes me roll my wrists forward to properly acquire the target. Personally I don't like it, so I'll stay with my XD, HK's and S&W's.

Reliability wise, Glocks are excellent, very accurate, and you can buy a grip angle reducer. Lots of accessories are available as well.

I've shot a few thousand rounds through them, mostly the model 22, as they were the primary weapon we trained with, although I was allowed to carry my S&W 4006 and 5903 on duty. We had to learn how to operate every weapon.

The three pistols you have a choice between are all full sized, and with some very minor differences, essentially the same size so it is a caliber question. For me, .45 ACP, .40 S&W, and then 9MM in that order. Bigger bullets usually stop the fight much quicker, all other things being equal.