Hi - I haven't stayed at either; we live on Cape Cod, so I just wanted to mention if you have it narrowed down to both - Brewster Green isn't really near the beach. You'd have to drive (maybe 5-10 minutes) and pay ($10 - $15) to go to the bayside beaches. It's a beautiful resort, lovely area, but frankly I always thought they were retirement homes, not a vacation resort! (We live near Brewster Green and I've driven by the end of the street many times)
If you're really looking for beach, the InnSeason are right on the beach, so you'd probably prefer that - and honestly, if I were going to vacation on the Cape I'd choose to be right on the ocean. That being said, make sure you check tripadvisor for a few reviews, just in case.
Good Luck with your vacation!