A 16-gauge is harder to locate and to find shells for outside of certain "hot spots" in the country, mainly in the South. So, one may sell for less than a 12 or 20.
Personally, I wouldn't buy a 16 unless I got a really cheap deal on a nice one. Others really like the gauge, though.
Same for the 28 gauge.
The M-37 is certainly a classic pump shotgun. I like the location of the slide release, handy to the trigger finger.
Some don't like the bottom loading and ejection. And the guns are light; they kick. I've heard some recoil complaints. That probably kept them off of clay target fields. But hunters often like the M-37. (But presumably, not dove hunters in Argentina, where they may fire many shells in a day.)