Yensid,
All I can tell you is what happened to us in our limited experience last year.
First we only went to the theme parks on one day which was Monday of Tgiving week and the it was the Magic Kingdom. I would highly recommend using the touring plan that best fits you and your family that is listed in the book "The Unofficial Guide to Walt Disney World". They are summarized in the back of the book. Our public library had several copies and I got it and photocopied the plan page before we left.
It ABSOLUTELY helped us get on the rides with the shortest lines possible and of course we worked in Fastpasses as well. In fact it worked so good I felt like I was surfing in front of a really big wave because when we would get in a line it would be short, we'd ride the ride, and when we got off the line had gotten so much longer. I felt like everyone was following me!

We rode Space Mountain, Buzz Lightyear, Pooh, Peter Pan, Small World, Haunted Mansion, Big Thunder Mtn, Pirates, had lunch, Splash Mtn, and Jungle Cruise all before 130pm. Of course you need to take the first boat to the MK (leaves the FW dock about 30-40 minutes before opening) to be there when they open the gates.
I'm not into a highly scheduled day in the theme park but we knocked out the biggies then had time to drift around. Country Bears, Tom Sawyer Island, ride the train, HoP, browse the shops on Main Street, etc. Space Mountain had JUST reopened after its long refurbishment and the listed wait time was over 2 hours!

The folks who publish the Unofficial Guide also have a website that lists estimated wait times/crowds in the Disney Parks and it will show what to expect. Here is the link
http://www.touringplans.com/tp2/UG2_index.php?PageID=14. Use it along with the weather forecast, family wants, etc to make at least an informed decision of what day/what park/what rides. The plans all focus on the fact that the extra hour days (EMH and whatever the evening one is called) actually create bigger crowds and longer lines so they nearly always avoid the park that has the extra hours any given day.
I'm on vacation to relax so I choose the lowest stress route to visiting the theme parks. If you are a theme park warrior, an uber-Disney fan who has to ride every ride and checks them off the list as you do, my advice is not for you. I can't tell you about the crowds later in the week because we didn't go. But the Monday afternoon at MK was hot and crowded.
Good luck with whatever you decide.
Bama ED