i don't think you can go wrong with either one. for me the negative for wl is the fact that they're so close to mk but you still have to either take a bus or slow ferry to get to mk. negative at the poly is the crowds that their restaurants draw.
I know both resorts, stayed at the WL in 2007 for 4 days and in the Poly in 2010 for 5 days and I loved both. However the WL has smaller rooms than the Poly but they have better housekeeping at the WL.
The problem with the WL is, that also it's a MK area resort it has no monorail. You have boats to the MK and buses to MK and the rest of the World. The monorail at the Poly is a BIG perk but when I was at the WL the bus transportation was very reliable and fast.
Both resorts are WDI-theming at it's best, it is really hard to say which one is better, the Polys lobby is a beauty, but the WL lobby is nothing less than overwhelming and breathtaking! It's a place where you can sit down and let the time go by and do people-watching. The pools in both resorts are beautiful but the volcano pool at the Poly is still more impressive than the (smaller) pool at the WL. BTW both pools are too small considering the size of the resort but that is a major design problem with most deluxe resorts.
If you stay at the WL it's a little like staying in Yellowstone or Yosemite NP but WDW is only a bus trip away, if you stay at the Poly it's like staying in the South Seas but a boat or a monorail will bring you to the MK in less than 5 minutes.
Both are great.
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