I prefer the AKL as a resort. It's so different from anything I'd ever been in before. The theming is magnificent and all the educational programs at the resort are really cool. Once indoors, the Poly looks more like any old hotel; however, the rooms are bigger.
AKL is less expensive. I booked room only with a code and got $129 a night (standard view with bunkbeds).
AKL has a huge pool, but the water slide is pretty tame. Poly has a smaller pool, but my kids liked it better.
What cinches it for me, though, is the transportation. The monorail to MK and Epcot is so much nicer than the long bus trips from AKL. If money isn't an issue, do the Poly.