Hi!
We've done both and like them both very much. I would say the rooms are pretty comparable.
There are not many standard view garden wing rooms at the CR. They have a view of the parking lot. THey are the least expensive rooms among monorail resorts, they they book quickly. If you want one I would book early. You can always add a room only discount to your reservation later if they come out later. There are also "garden view" garden wing rooms at the CR. THey have nicer views but are more expensive, but not much more.
At the POLY, garden view rooms are more available.
The difference between the two is mostly theming. Poly is more relaxed and resort-ish. CR is more "bustling city. " I like them both alot. DH does not care for the theming at CR, but he really likes more nature, trees, etc. I find CR a little more convenient to get to from the MK, because you can always walk no matter how crowded it is, especially at closing of MK.
Regarding a discount- I have gotten 40% off at the POLY and/or CR for three years, but the discounts just weren't as good this year. THey haven't discounted the monorail resorts as heavily as some other resorts lately. But they may come back. You never know. I am hoping for a nice discount at POLY or CR for late next year, myself!