I've stayed at the Mariott and PP - both were very nice. The Mariott has more of a resort feel to it - larger pool, etc - but PP is Disney. If it was my choice - I'd go Disney!
Of those 3 I've only stayed at PP. For the price difference that would be my choice of the 3. Staying onsite will get you more days of EE then the 2 off site, and its closer.