What is it about the Poly specifically that you like? The theming? The easy access to MK? The pools? The restaurants? The rooms themselves?
None of the off site hotels has the kind of theming the Poly does, and you'll have to bus or drive to MK.
The Swan/Dolphin has the best location - walking/boating distance of Epcot and HS. The rooms are nice, and it has good pools. Be aware that the Dolphin has 2 double beds, whereas the Swan has 2 queen beds, but the prices fluctuate so that sometimes the Dolphin is more expensive. The Swolfin also has (limited) character dining.
Depending on how much you want to save, you can book at the Disney Springs hotels for much less than the Swan/Dolphin, and still enjoy 60-day FP and EMH, but the hotels themselves range in how "nice" they are. Some like the B are more upscale, but others are much more ordinary like the Holiday Inn. While they all have pools, none is really resort-like with the kind of extensive pools you'll find at the Poly. You don't say how many are in your party, but if it's an adult trip, something like the B might be nice. If you have kids, I believe two of the others (can't remember which) have character dining. There's a great shuttle bus to the parks, and you're walking distance to the Disney Springs shopping, dining, and nightlife.
If you want more upscale resort feel, something like the Waldorf Astoria or the the Hilton Bonnet Creek (share which are next to each other and share onsite amenities) might be worth a look. No EMH or 60-day FP, but definitely great pools, upscale rooms, and great shuttle bus schedule.