I've stayed at the CR/BLT (and just bought there) (2 weeklong stays), and also GF lagoon view (1 week). We've visited the Poly a lot on all of our trips to GF and CR, but have not stayed there. If $ were no object, GF would be our choice (and our 6 year old's!) for the following reasons:
Restaurants - there isn't a bad one at the GF, and there are more there than anywhere else. I have enjoyed or will enjoy ALL of the TS restaurants: V&A (going in August), Narcoosee's, Citrico's, Grand Floridian Cafe, 1900 Park Fare, and the QS is a guick step away to sit outside with a peaceful and beautiful view. We've done Ohana breakfast (fun, but noisy and so so food) and also Chef Mickey's (too loud, bleh food). GFC >> Wave. I do like Kona Cafe (and California Grill) a lot, but each of those alone doesn't beat Narcoosees + Citrico's + GFC, and V&A is another thing entirely.
Rooms/Resort layout - I've never stayed at the poly, and have only seen the pool, not used it, but: the longhouses feel a little like dressed up 70s style motel rooms, and the CR just feels convention-y, loud and crowded. Many lagoon views at GF have really great views of the castle and fireworks, which we watched from our balcony while the baby slept. BLT felt like a nice apartment building. Because the GF rooms are spread among several buildings, there is never a big cluster of people in any one location, unlike both CR and Poly lobbies.
Location - you can use WDW transportation to get to any resort or park at WDW, thanks to the MK bus depot. And you can walk to MK. With little kids in strollers, that's just ... amazing. Poly has TTC so easy access to EP and MK without having to switch monorails. GF - 1 easy stop to MK, and walkable to Poly. Each has merits. This is probably a tie, with a slight edge to CR because we have little kids in strollers.
Overall atmosphere - I like contemporary design, so I actually like the design in the CR/BLT rooms. I also thought GF would be stuffy but it wasn't. Really lovely service and CMs who went the extra mile. There's just so many touches that make it so magical - for example, my DD (4.5 at the time) was wearing an Aurora dress in the lobby by the pianist and he broke into the Sleeping Beauty Waltz. When we stayed that the CR, sometimes I would walk to MK while DH stayed with the kids at naptime. At the GF, I walked around the resort and shops instead. And the Princess promenade (or whatever it's called?) is the only place to see Prince Charming on a regular basis for free.