We have just returned from a two week stay at the CR, GF, and Poly. We have four children and our youngest is four. We had a fantastic stay and really liked all three resorts. My short answer is the Poly but I think it's purely individual. My long answer is well, ALOT longer

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CR: We really liked our rooms here and while we thought the view was great we actually thought the fireworks view from our room was good at all three hotels. We loved being able to walk back to the hotel when the monorail was busy but didn't miss it when we changed resorts. CR is the first stop on the monorail at the end of the day, from the Magic Kingdom, which is also nice. We felt the atmosphere here was busy and bustling. Chef Mickey was fun and the grab and go was convenient. Also, if you plan to do Hoop-de-do we found the boat from Fort Wilderness directly to CR after the show was less crowded and faster to take than the boat to MK where the other resorts pick up their guests. We just hopped right on the CR boat and then took the monorail back to GF - super easy and fast! With a stroller it was slightly easier here to get on the monorail. If you are in the main tower you can take the elevator to the monorail floor and then you will take either the escalator or a small elevator to the monorail platform. You will not need to leave your building, the way we did at the Poly and GF, then go to the main building and get on the elevator to go up to the monorail platform. A quick note about our rooms (at all three resorts) - there is a latch (placed at adult height) on the sliding door to the balcony that prevents little ones from opening the door and I was very appreciative of this. Now, I know this is strange but the toilets in our room had the loudest flushing sound ever and our youngest daughter refused to be anywhere near the bathroom when it needed to be flushed because she thought it was scary. The sinks do not drain easily and while this is a small thing it was actually fairly inconvenient for us. Finally, our four year old never really noticed or cared that the monorail went through the building but our older ones thought it was cool. This was our twelve year old's favorite of the three.
Poly: We loved our rooms here! To be perfectly honest (no flames please) I didn't think I would like it here when we went past it on the monorail - I saw the orange roofs and thought mmmmm....maybe not - but WoW! Did I change my opinion once we walked into the lobby to check in! We felt the atmosphere was in between the tranquility of the GF and the hustle and bustle of CR so, for us - just right! The pool was very nice and we enjoyed Captain Hooks for quick snacks and meals. The Lilo and Stitch breakfast here was excellent! We found it easy to walk to the TTC and the GF. We also felt it was slightly easier to take the elevator to the monorail floor here that at the GF. We felt it was a more "Disney immersive" experience to stay here than at the CR - I don't know why! We also thought it was fun to take the boat from the hotel straight to and from MK. We found it was actually sometimes faster to do this than to take the monorail in the evening. Also, we had a view of both the fireworks and the evening water show from our room. We thought this was wonderful when our littlest ones were tired - they could rest while we just opened the curtains and enjoyed the view! Our only negative was that our room was a bit dark and we felt we could have used a little more light. For us, this was our favorite of the three (with the exception of our 12 year old). We enjoyed the atmosphere at the Poly the most and felt we could really relax here after a busy day at the parks.
It's a totally personal decision and both resorts are nice - honestly! We went from the CR to the GF to the Poly and each time I didn't want to leave because I thought the next resort wouldn't be a nice (at the Poly I just didn't want to leave)! I know it isn't helpful but it just depends on what you and your family prefer - modern or tropical, bustling or peaceful, walk to TTC or MK, basic pool or themed pool, etc. Whichever hotel you choose you will have a terrific time!
