A person, yes. 9mm is absolutely adequate for defending yourself against people, and even .380 works pretty well. 99% of the time, the correct answer for self-defense is something like a Glock 19, and a lot of time at the range and dry firing.

For hunting mid-sized game (pronghorn through elk) or as a bear defense weapon if you hike in grizzly or kodiak country, bigger is generally better, as long as you can shoot it accurately.