Depends on a couple of factors such as whether you want 720p (Polaroid XS7) or 1080p (Samsung W300) or the depth at which you will be recording underwater video (30' for the Polaroid and 16.4' for the Samsung). If you ever plan on using one as a helmet cam or want to mount it on a bike, car, etc. then the Polaroid is the way to go between the two of them.
Reviews:
Polaroid
http
/camcorders.reviewed.com/content/polaroid-xs7-first-impressions-review-updated
http

/www.amazon.com/Polaroid-Waterproof-Sports-Mounting-Included/product-reviews/B009ETEEAU/ref=dp_top_cm_cr_acr_pop_hist_all?ie=UTF8&showViewpoints=1
Samsung
http

/camcorders.reviewed.com/content/samsung-hmx-w300-review.htm...