This is a common question from students. Unfortunately, with one exception, the answer is not easy. The simple answer is the gun you will carry and practice with. Other than that…well, it gets more complex. Most of us started at the range, trying different calibers, models. What fits my hand may not fit your hand. Some like revolvers, some like semi-0 auto, some like 1911. I’ve seen slim women effectively conceal a full size .40 and other struggle with a mini.
First step is what you are comfortable shooting. Once you have your firearm, then look at your attire, and holster combinations. One of the keys to effective carry is consistency. As much as possible carry in the same place every time so you can practice with and avoid the gun pat, the act of reaching for your gun and realizing it is not in your normal position and you have to pat yourself down to find it.
Strong side hip has been a go to for many years, for good reason. Think, for a right hander, generally 9:00 position on the body. It allows consistency and easy access. There are a lot of great hybrid holsters, leather against the body with a kydex shell for your gun. Appendix has been gaining popularity lately, think approximately 7-8:00. Understand that these options require a good belt. Not a soft little fashion accessory but a serious heavy supportive leather.
There are other options more unique to women. There is the Bra holster (Flashbang is the often copied original). I have friends who love it, and some who hate it. It is personal preference. I have a sport belt from Can Can Concealment that allows me to carry my gun, a spare mag and my id securely under mot any clothing, no belt required. Can Can also makes a sweet lacy garter holster, and you can get a belt with garter straps for extra security. This works great under a dress, it grips pretty well but I do prefer the straps. On a bet I did conceal a Desert Eagle in one, but it wasn’t comfortable.
The last option I want to offer you is my least favorite. Purse carry. It is my least because it is off body which requires extra attention and care. You can’t just hang your purse on a chair, you have additional responsibility to maintain the security. Key point is the difference between a carry purse and purse carry. NEVER toss your gun into your purse, it is dangerous. You can’t maintain the position, and security of your firearm. A Carry Purse contains a compartment that is dedicated to holding your gun, it usually contains a velcro system and holster along with opposite ends access to you can carry on with shoulder. But once you choose a shoulder, you are stuck with it as the gun won’t access well from the barrel end. Carry purses come in a variety of configurations, from simple pouch to high end leather, prices accordingly. There are also backpacks and briefcases with built in carry systems. They can be effective, but not my first choice for carry as it is off body, and if you are mugged, you lost your gun. However, there are times when it is the easiest option. Generally the compact and mid size fit best. Just always remember you are responsible for the bag and the gun.