luckytso,
I guess the WDW and DL comparison will always be the "great debate," but personally, I think of them as two separate entities with their own personalities and identities. I've been to both, and while I love WDW and would go there every year if I could (I live in Hawaii, which makes it costly), I still love going to DL and usually go there when I can't make it to WDW.
I don't think you'll be disappointed with GC either. I'm a WL lover, and I completely fell in love with GC when we stayed there! We spent lots of time just looking around the hotel. When you go there, you might want to ask Guest Services if they've come up with a Hidden Mickey clue list. I know the hotel is filled with them (they cover a couple during the tour), but when I asked for a list they said, "not yet, but they might be working on it."
Also, if you can squeeze it in, we really enjoyed eating at Storyteller's Cafe. We had the breakfast buffet one day (character breakfast with Pluto, Chip, and Dale) and dinner another. They have a dinner buffet, which looked really good, but we wanted a light dinner so we ordered off the menu. The corn chowder was excellent!! If you're looking for a good character meal, I've heard great things about Goofy's Kitchen. Whitewater snacks has an excellent breakfast sandwich, for less than $5! They don't actually call it a sandwich, but it's a huge biscuit with eggs, bacon, and cheese.
The other thing I think is different about DL is the DD there. I love WDW's DD, but DL's is very different. Also, I actually prefer the restaurants in DL's DD. For some reason, practically every restaurant we tried in WDW's DD really disappointed us, except for Portabello Yacht Club. At DL, it was quite the opposite! Just about everything we tried was excellent!
And along the lines of Jlima's comment, there are many people who will tell you that DL is somehow (unexplainably) more magical than MK is!