B+T APC9
If you are familiar with the NFA paperwork making it a SBR won't be a problem.
Easy platform to learn, low recoil, light weight, and easy to suppress being basically just a fancy blowback 9mm.
Yes, its on the high end of the price spectrum, but, that's secondary for what it's job is going to be.
We don't have the option to SBR where I live so my wife runs an AUG. We would have a second TP9 if we didn't live in Illinois, and will be, for the foreseeable future.
Once you add in the application of the weapon for self defense, everything changes. I sold the AR-180B, the Century AKs, the SKS, and the Saiga 12 and bought the AUG. I don't own any firearm, save for the .22lrs, that I don't trust as much as I can trust a mechanical device. When I realized that I'm not going to be wealthy enough to be a collector I realized I would rather have quality over quantity. That comes with a price and my wife's well being is worth the nearly $3000.00 investment after the weapon, optic, light, magazines, and ammunition to become proficient in handling the weapon when it really counts.
And God damn, does she have a good time showing guys up on the range in the short time she's been running it. Being comfortable with the weapon is critical.
When I'm gone our American Staffordshire Terrier (that's a Pit for all the haters) should give her enough time to get to the AUG and its 42 rounds. Turn on the light, put the dot on the target, and keep shooting. Call the cops if you have time.