9mm offers the optimal balance of factors: affordable practice ammo (half the cost of .45 ACP), manageable recoil for faster follow-up shots, high magazine capacity in compact packages, and modern hollow points that match larger calibers in terminal performance. It's the caliber used by most law enforcement agencies worldwide.

Beginners should look for a full-size or compact 9mm with a polymer frame for lighter weight, a striker-fired action for simple operation, and a capacity of 15+ rounds for range practice. The additional weight helps absorb recoil, making learning proper fundamentals easier.

Higher capacity provides more rounds before reloading, but comes with trade-offs: larger grips may not fit smaller hands, and longer magazines can print more during concealed carry. Match capacity to your use case - home defense benefits from max capacity, while CCW may prioritize concealability.