We go to WDW at least once a year (usually in Sept) and are APH at DLR. Just went to DLR last night for about 5 hours.
We don't spend much time in MK but there are a few things there you won't see in DLR.
Carousel of Progress-for me it brings back memories of when it was at DL.
Hall of Presidents-has all the Pres. not just Lincoln
Mickey's Philharmonic.-GREAT!
Fireworks-Grim Grinning Ghost Spooktacular if you'll be there during
MNSSHP
Tiki Room-under new management. Better than the one at DL.
Rides that are similar, but better at DLR.
Pirates
Space
Splash
Small World
Similar but better or at least as good at DLR.
Buzz
Haunted Mansion
Rides not at DLR but at MK
Goofy's Barnstormer in Toontown. Pretty fun for kids but DLR TT is better overall.
That's basically it-I'm sure I forgot a few.
For us, our favorite parks are Epcot and Animal Kingdom. DD10 was just saying yesterday that Epcot is her fav. park, but she doesn't know wjy (I do, it's called Test Track!) In Epcot you can skip Soarin' if you've done it at DCA if it's too crowded. It's exactly the same. But not to be missed is Test Track and Mission Space. DD also enjoys check out Innoventions East and West.
At AK not to be missed is Expedition Everest, Kilimanjaro Safar (try to ride in the a.m. and near closing), Festival of the Lion King, Nemo show, Dinosaur (sim. to Indy ride at DLR, but different), and if you have young kids-check out the Boneyard-DD still loves to dig around in the "dirt" to uncover a dino fossil.
DHS is the park we probably spend the least time in. ToT is a definite don't miss though as is Rock 'n Rollercoaster. Also good is the Indy Stunt Show. The Beauty and the Beast show is good, but not as good as the show DL used to have (which lead to the B'Way version). You can skip Catastrophe Canyon-pretty lame. Star Tours is the same as at DL though the one at DL closing next month for refurbishment (going 3-D) so the one at WDW may be too.
Though the 4 theme parks are fun, for us, since we go to DLR quite often, our favorite parks are the 2 water parks. And the fall is a great time to go-still hot enough to go but the crowds are less. Last year we went to the waterparks 3 days (instead of our normal 2). I think we did the other parks a total of 4 days-with alot of parkhopping.
Re: park hopping-the 4 parks at WDW are pretty far apart. Nothing like the 1 minute walk from DL to DCA. Know that if you park hop you will loss time. More if you use Disney busses than if you drive. Hopping between MK and Epcot is pretty easy, though you do have to switch monorails at TTC. You can boat from Epcot to DHS. AK is only accessible by bus.
Our hearts belong to DLR but we LOVE going to WDW! Absolutely love it. We spend 8,9,10, 11, or 12 days when we go (counting travel time) but we do explore the "real" Florida as well. Not all our time is spent in the parks.
Dining can be a huge thing at WDW. If you are doing any TS book them as soon as you know where you want to go.
Have fun!