I have been legally concealing a firearm since 1987.
The biggest mistakes that I see made by folks new to carrying concealed firearms are first considering that law enforcement officers self defense needs are congruent to civilian self defense needs, as they are not and selection of a bloody hand cannon that makes concealment difficult and carrying a chore.
The point about not being law enforcement should be considered. As civilians, we are not legally or morally obligated to stop malfeasance that is not directed at ourselves or our family. In fact "getting involved" might end up with you having to defend your liberty in a court of law. For instance, you're in that Shop-N-Rob gas station when it gets, well, robbed, in most parts of the country you may not uncover your firearm until YOUR life is threatened and I would add that you had better be able to demonstrate that threat to your life to a subsequent jury. Law enforcement can point firearms at people, civilians may not. In much of the country civilians have a legal power of self defense but I would add that power does not extend to us sheepdoging, intimidating otherwise pointing that firearm at others.
My point about hand cannons. How many times have I been in a gun store, gun show, read a gun magazine or online expert expand on what gun a person MUST carry to be ready for every situation. Many folks get sold the same full sized hand gun that the local law enforcement carry. The supposition is that LEO carry guns all day so they must be experts. The reality is that many LEO carry what their department attorney has found acceptable to insulate the department from liability or worse, the best deal the department could work to equip everyone. The truth is that most LEO about as much about firearms as they do about the flashlight or handcuffs on their belts. Do they know how to use these objects? Yes, but does that make them experts in flashlights, handcuffs or handguns? Absolutely not.
The best, hard learned advice that I can offer is to first sort out HOW you will carry a firearm and then sort out WHAT firearm you will carry. This was a long journey of experiences and learning for myself. My journey included wearing suspenders instead of belts thanks to diabetes. My journey included several spinal and knee injuries that limit where I can physically carry a handgun. All those great but large handguns that I have carried concealed in the past, M1911, GP35, P226, P229, 66, 629, G17, M&P9, M&P45, P220 etc just did not work out as planned. Because I am not a cop and do not HAVE to carry a handgun, these large cannons ended up being awkward to carry, impossible to sit down with and generally complicated my life. My spinal injury made it less painful to carry weights below the injury. More often than not I found myself slipping a hammerless S&W revolver into my pocket along with a few Bianchi speed strips in a different pocket. Stuck in a DeSantis pocket sleeve, this was so comfortable that it always came with me when I stepped out. The system that I have used since at least 2000 is that I walk about with this seemingly inadequate sidearm concealed one my body, while I have in the vehicle a much larger, more competent firearm concealed in a cross-body style concealed carry bag (maxpedition, 5.11 Helkon, etc). In the last 15 years or so I have pocket carried a Glock 19 or Shadow Systems version but these are really too much for my spine. I normally carry an original version of the S&W Shield in 9x19mm. I can shoot this better than the J frame and this does not have the cylinder bulge. If I am going somewhere where I anticipate that I might encounter a natural animal threat i carry a Glock 40 in 10mm Auto.
Concealed or open carry? That's the wrong question. That choice is quite personal to the individual and their needs. What legally works for you, in your situation, is fine by me. The better questions are what firearm actually suit YOUR needs and HOW is that firearm going to be carried in such a fashion that it does not get left at home.