Wow! FREE hotel rooms - now that is worth considering. Those are really busy days, but with the money you would be saving on hotel rooms you could buy an Express Plus pass for every day. I haven't personally used this, but people have reported good luck with them. This is a pass that you buy (probably $25 each for those dates) and you can use the Express line once per (most) attraction per day. Each person in your party would need a pass. You could also utilize the free Express Passes that are available in the parks in addition to the Express Plus. I hear these (free ones) run out fairly early in the day for popular attractions, though.
That being said, my family really enjoys staying onsite. You do have to consider the cost of Express Plus passes and daily parking ($8 or more, I think) to decide which would be best for you. Staying onsite is really fun and convenient and you have unlimited Express line priviledges.
There are others on this board who can give you more specific information on prices, etc. and links to helpful info. I am not good at the "link" thing!
We were in the parks on your dates last year and the crowds were quite large but that sort of added to the fun. The decorations were beautiful and the parade, Grinch, etc. were so much fun!
You will have a great time whichever option you choose!
Nan