I stayed at Poly as an escaped fetus, but have no recollection of it.
However, I have decades of memories of being a Shades of Green parasite that walked through Poly's lobby, used its Monorail station, and ate at its restaurants. Poly is awesome!
That said, I think Yacht Club is nicer 10 days out of the week. The pool, immediate access to two parks (that's more convenient than Poly's access to one), and just the absolutely gorgeous Boardwalk at night, hard to knock it. Easy access to Topolino's if you want an excuse to ride the Skyliner (if you prefer walking to Hollywood Studios)
Personally, ignoring the savings, I easily prefer Yacht.
Depending on what I'm looking for in a Disney Hotel, here are my thoughts.
Best location: Yacht & Beach
Best theming: Animal Kingdom Lodge
Best theming honorable mention: Wilderness Lodge
Best monorail: Poly
Best pool: Yacht & Beach
Best all around: Depends on the trip.
Best value: Skyliner resort of your choice
If I want to exclusively enjoy the hotel, AKL is easily my top choice, the Savannah coupled with incredible food and theming makes AKL insane. On a Magic Kingdom dominated trip, Poly might make the most sense. Wilderness Lodge feels the most secluded, so if you want isolation, but easier park access than AKL (AKL's biggest downfall). But Yacht's location, proximity to so much of interest outside of the parks, theming, and INSANE pool, it's hard to beat. After this past trip, we had a split stay at Dolphin and Yacht, and honestly, I don't see us staying outside of Dolphin anywhere in the near future, I just love the Epcot resorts area and Dolphin does a fantastic job of pleasing us.
Yacht is definitely nicer than Dolphin, but we normally don't make sufficient use of its pool. In totality, Poly is awesome, but I think Yacht is just even greater. I think most of the perks at each hotel can be achieved by resort hopping (AKL, WL, and Poly all have great environments), but unless you're staying at Yacht, you don't have the location and pool, items you can't makeup by resort hopping.