We kick start with the variants. The Gear S3's two variants were named, 'Gear S3 Classic' and 'Gear S3 Frontier', while Gear S2's (also two) were named 'Gear S2 Classic' and 'Gear S2 Basic'.
Of the two models, the biggest, appears to be the Gear S3, with a 46mm size, it may not fit the small-wrists folks. They (Small-wrist folks), however, remain covered, as it appears that the Samsung Gear S2, was developed with them in mind; a smaller wrist size of 20mm.
While S3, can be perceived as a watch appropriate for a dress (owing to its leather strap), the S2, took more of the sports-watch look; of course, owing to the sporty looking plastic curves.