I read a post you made the other day about taking your parents to a resort you already know and love. Stick with the Poly. You can get adventurous on your future trips with the kids.
I will be staying at the Poly,the week after Thanksgiving..Im so excited and remember The Poly is almost like an Epcot resort as well,with the monorail access to both parks being an option...
I vote for the Polynesian. The Dolphin in not an "official" Disney resort. Things are just a little different there. It is nice, but I wouldn't try it for the first time with guests.