I have stayed TPV outer building. It was lovely. I did not pay for this, I was bumped up and accepted the upgrade gladly. I have to say that the Grand is a gorgeous resort that seems to be a bit formal from the outside looking in, however it is far from that once you are there. I absolutely love this resort, and was pretty tickled when my then 15 YO DGD informed her Mom and Dad that while she was happy to be at the Poly with them, she was really a "Grand Girl" like her Nana! LOL!!!
The outer buildings are really a Godsend IMO. I liked the walk to my building, no matter which one I was staying in, becuase it offered a transition from Park mode to "Welcome Home" and serenity. The entire resort is tranquility, from the manicured gardens and grounds, to the music plaing in teh common areas. The lobby is a treat inteh afternoons, with the Grand Pianist entertaining and little Princesses dancing to teh music in their own "ballroom." I brought my Princesses here just for that lobby and it was worth evey penny. They insisted they were in their own Castle.
My son in Law hated it, and my DD only tolerated it, and I would chew glass and die before I booked it with my DH. Me and Kady? Our preference!
WIth that said, the Poly is awesome and offers a different kind of vibe. It is a tropical paradise, and also has longhouses away from the Grand Ceremonial House so you can walk away from the crowds. I would choose a longhouse that is not centrally located if you want to get away from the many people coming in from the boats and monorail. My DD and her family were in Areotoa (sp) and faced the monorail. At first she thought she was going to need to ask to me bored, but it was a wonderful space. The monorail whisked softly outside the balcony, but was no disturbance. They just had a short stroll to the marina to enjoy their own "private" beach.
Choose your resort based on cost, theme, and amenities you will enjoy. Both the Grand and the Poly are excellent choices for a monorail resort stay.