Hi K.,
I haven't stayed at either, but I've eaten dinner at both multiple times. I love the feel of the Poly - it's laid-back and reminds me of Hawaii. And they have some great restaurants, and a beautiful beach! However, my husband DOES think it looks run-down, which is why we've never stayed there. I can tell you that the Poly has the highest return rate (of previous guests) of any Disney resort, so people who give it a chance definitely like it!
GF is beautiful, but it's too ...well, for lack of a better word, stuffy for my tastes. We haven't been there since we had kids, but even when it was just my husband and I, I remember feeling like I needed to whisper whenI was in the lobby because of its formality.
The Poly has an awesome pool with a neat volcano feature, which I think is more enticing to kids. The GF pool is nice, but more on par with an adult luxury resort.
It took me a minute to realize what you meant about the Poly being near the monorail to Epcot - you mean that it's within walking distance to the TTC, is that right? It is, technically, and I've walked it before, but if you would prefer the GF, it's not going to make that much difference. You'd just ride the monorail from GF to the TTC and switch trains there. That's more fun than walking anyway! :-)
Hope that helps - good luck with your decision! When are you planning to go?
N.