Customized Full Size M&P 9mm V1.
1. 100% reliable
2. Very accurate
3. Easy to shoot well
4. Normal capacity on board + hi cap back up
5. Easily concealed AIWB
6. Parts, accessories, and holsters are easy to find
7. The caliber has adequate power, easy to find, and has many options for training and carry rounds at reasonable (relatively) prices. I carry Barnes TAC-X 115 grn hollow point all copper bullets.
Each individual's needs and capabilities are different. I carried a smaller gun in Thunderwear when I wore a suit for work every day, often removing my jacket. Now that I am retired, I wear untucked shirts to cover the larger pistol. I find AIWB conceals easily, it's fast, it's controllable, and (hopefully without starting a mis-direction side thread) IMO it is the safest way to carry well concealed (over six years now).
I chose an RMR with co-witnessed iron sights as a fast sighting system that allows me to focus on the threat and get good, fast hits. I almost never see the iron sights. I cannot focus on a front sight any more.
I do have a V1 Shield 9mm set up similarly, and it carries even easier. Because it is smaller and recoils more, I don't shoot it quite as well as the larger gun. I carry it less than 5% of the time. I think the Shield's a great carry gun for many people, however, it is interesting at the range to share with other shooters how I carry the larger pistol. They are always impressed.