Gordyt is absolutely correct. This is what I learned while doing what he recommends...
When I first decided that it was time to really carry every day, I read the gun mags and talked to friends at the range, and started out by buying a Glock 36 and a Kimber Custom Classic. I shot and carried both guns a lot, both for practice and in IDPA.
After a couple of years, and one Gunsite class, I decided to see if my speed and accuracy favored one gun, or one carry mode over the others that I commonly used. I went to the range with my timer on several successive days, and shot hundreds of presentations to test both speed and accuracy for 1) G36 versus 1911, 2) IWB versus OWB, 3) Kydex versus leather, and 4) no cover garment versus vest with a weighted pocket versus shirt.
The timer and targets told me:
1) There was no speed or accuracy difference between Kydex and leather for the same carry mode (IWB versus OWB).
2) Inside 7 yards, there was no accuracy difference between the G36 and the 1911. Outside 7 yards, the 1911 had a slight accuracy advantage (both wore stock sights).
3) OWB Kydex was 0.04 seconds faster than IWB leather on average (time from beep to first shot).
4) Splits between first and second shots were exactly the same (G36 stock trigger versus Kimber stock trigger).
5) Having hand on the grip at the beep was fastest to first shot, followed by hands at the side with no concealment garment (0.50 seconds slower than hand on gun), followed by hands at the side with vest concealment (0.60 seconds slower), followed by hands at the side with shirt concealment (1.01 seconds slower).
6) My personal reaction delay is 0.24 seconds (measured by gun on target, finger on trigger, time between beep to one shot).
Of course, your mileage may vary.
This was terrific exercise for me, however. Based on these results, I decided to carry the G36 all the time, IWB (in Milt Sparks Versamax 2 Horsehide), and to focus my tactical mindset on ways to get my hand on the grip before having the draw if at all possible. I knew that this decision penalized me a little at distance and minimized firepower, but I figured that the extra concealability was worth it. I also decided to carry a spare magazine with a +2 round extension that would help both issues.
I would still be carrying that G36 today, except that it broke four times in my hands. Three times a pin holding the trigger assembly in place sheared (each time inspected and repaired by a Glock armorer), and once the entire recoil spring assembly failed. Each time I was left with a club in my hands. I also slowly realized that I was getting good at performing malfunction drills because I was experiencing too many FTEs and FTFs in practice and IDPA with the G36.
After slowly realizing that the G36 wasn't reliable enough, I looked around at the IDPA shoots, and realized that those who were shooting full size or compact XD were not having ANY malfunctions or breakage. I tried a full-size XD45, found that it fit my hand, and bought one. After really testing the XD and getting holsters/magazines/etc., I sold the G36 (and all of the mags and holsters I had accumulated) and have stuck with the XD45 since. I now have two XD45s and an XD9 that I shoot a lot.
I have NEVER had any breakage OR a SINGLE type I, II, or III malfunction with any XD45 or with my XD9 with factory ammo or my reloads even though the round count is much higher with these guns than I had on my G36 or Kimber. I now carry a 4" XD45 compact (10+1 versus 13+1) every day IWB in a Sparks V-MAX 2 with a 13+1 spare magazine, and couldn't be happier with my choice.
I apologize for the long response, but I figured that just giving you my choice, and not including the rationale, wouldn't be worth much.
The XD isn't sexy and doesn't photograph well, but it fits me perfectly, shoots a serious round, has adequate firepower, and has always performed reliably, with a broad variety of ammo types. I couldn't ask for anything more.
I've found that the most valuable accessory in my range bag is my shot timer. If you're serious about carrying, and being effective with your choice, get some professional training, and practice, PRACTICE, PRACTICE with your equipment, with a timer, so that you get real feedback on your performance.