16" is a child's saddle nowadays. They are hard to resell and they have usually low resale value, except maybe some elite French brands. I would try to avoid a 16", unless the larger saddles chair-seat you. (That is what happens if the seat is too big, because the dip of the seat moves farther back with a longer seat but the stirrup bars are still up there in front.) Don't go too big, or it might be impossible for you to get your leg under you for correct balance.
A 16.5" is the small adult size. It will have much better resale value if you outgrow it or decide to upgrade or you need a different saddle later.
I am 5'1" and I could ride a 16" only when I was very very thin. 16.5" is my size in most cc saddles.
Try saddles on the horse, with leathers and irons properly adjusted, and pay attention to whether or not the stirrup leather hangs in the right place, is too far forward, or too far back. If you can't try it on the horse, then prop it up at the correct angle and tilt or level on the saddle stand. If the saddle is tilted either up or down on the stand more than it would be on the horse, it won't compare to how it will position you when it's on the horse.