Jyezahn
US Veteran
This is a purely subjective thing. Kind of like having 7 rounds versus 8. (Yay, New York) Get yourself into a habit, whether it be just EDC, range time, home practice. Then, once you have a habit, ask yourself what would be convenient to have (i.e. "it would be nice if I didn't have to reload my mags so much at the range", or "I have 3 magazines, but one never sees any kind of action and has been sitting in my bag/safe this whole time"), and go from there.