16 or 12 no big difference, and the 12 gause is obviously more versatile.

At one time, fairly ordinary 16 gauges and also smaller chamber 12 gauges were available for around $400 from a local gunshop, galore. The supply dried up over time. I considered one but didn't need it. Got enough 12 bores to kee me happy and can use more 12's.

A 20 gauge makes sense if one wants a really nice light shotgun, especially for a woman. Though 12's can do that too with the right one and right shells.

BTW I once used nothing but 1 oz/28 gms shot loads or maybe 95% of the time. Had a huge bag of 28 gm plastic shells/wads and hadloaded 28/30 gm shot loads. Worked fine. Shot better back then to now.