I agree with previous posters that WDW is more of a vacation destination in itself, whereas DLR isn't necessarily something I'd travel across the country for by itself but is instead just a part of a vacation that would involve other California-area attractions. We happily go to WDW and don't leave Disney property for a couple weeks, but I probably wouldn't spend more than 3 or 4 days at DLR. I love both WDW and DLR, but greatly prefer WDW.
There are a lot of factors to take into consideration when trying to choose one over the other:
- Weather. Lots of people love California weather, but I'm not one of them. I've been to Anaheim more times than I can count, and it's never been warm enough for me. (Mid-day might be okay, but I need a jacket in the evening.) Give me the Orlando summer heat and humidity any day. (Note that we've also been to Orlando during winter when we've needed jackets and pants, so it's not always blazing hot.)
- Resort size. WDW is about 50 times the size of DLR. It's hard to get across just how big WDW is to someone who hasn't been before. Some people like that they can quite easily leave DLR property (cheaper, non-Disney hotels and restaurants are very accessible), but I think the plethora of non-Disney establishments right across the street detract from the atmosphere and experience. WDW is much more immersive. However, exploring non-Disney attractions (other theme parks, restaurants) in Orlando takes effort (renting a car or arranging transportation).
- Park size and attractions. DLR is more ride/attraction-dense than WDW. Many of the same rides and attractions overlap between the two resorts, with some notable exceptions: DCA has Cars Land (reportedly one of the best-themed lands in all of Disney) and Paradise Pier (with California Screamin') that are not found at WDW, plus the Matterhorn and some other classic rides (like Mr Toad). WDW has Animal Kingdom (with things like the Safari and Expedition Everest), World Showcase, RRC at DHS, plus two water parks. Additionally, some of the rides that are at both DLR and WDW differ. For instance, the WDW versions of HM, ToT, and Splash Mountain are superior to the DLR versions; DLR has the better Pirates of the Caribbean, IASW, and Space Mountain.
- Non-park attractions. Besides the 4 parks, WDW also has 2 water parks, golf (mini & regular), DisneyQuest, fishing, boating, cruises, parasailing, etc, plus many more resorts to explore and restaurants to eat at than DLR. Plenty of people vacation at WDW without ever setting foot in the 4 main parks. Because DLR is so much smaller, there just isn't the space for all of those activities. There are much fewer restaurants, hotels, etc at DLR.
- Transportation. LA traffic is terrible, but once you're at DLR, everything is walkable. WDW transportation involves buses, monorail, boats, or rental car. I personally have no problem taking a bus between parks or park and hotel, but some people feel that it cuts down too much on park time.