Personally, Disneyland is my favorite theme park. It isn't my favorite "resort"....WDW is a better vacation destination when staying for a longer time. But if I could choose to go to any theme park, it would be Disneyland as of now (I haven't been overseas yet, so I can't say for sure it is my favorite park in the world...)
I would suggest going during the fall/winter holidays...because the place is all decked up...and simply because of Haunted Mansion Holiday. I loved that ride, it waas possibly my favorite there. But thats just me
They also decorate Its A Small World for the season. Its pretty cool.
There's a ton of more attractions there than in the Magic Kingdom, especially in Fantasyland...and I love the theming in Toontown, compared to Mickey's Toontown Fair.
The only down side of Disneyland as of now is its current Tomorrowland...there are a lot of attractions there that are getting kinda old...not to many "wow" features of the place...but even so, it does have both Star Tours and Honey I Shrunk the Audience...and seeing as both MGM and Epcot still consider those main attractions over in Florida, I'd say that says something about at least having them both in the same land. And of course, Space Mountain is great, but Innoventions and that Nasa thing are kinda time wasters...
The castle is much smaller at Disneyland, but just think about it this way....that castle is probably considered the gateway to all things "theme parks". This symbol stands for Disneyland, and in that way it also stands for the birth of true family destinations, cleaner environments in tourist attractions, and the construction of new, imaginative shows, rides, and other favorites we see at Disney and any other theme or amusement park for that matter, whether it be Universal, Sea World, Busch Gardens, or even Six Flags, or Cedar Park. I kinda see it as a landmark, more so than any other structure that still stands in any other Disney park, even more than Cinderella's Castle in the Magic Kingdom, regardless of how tiny it may seem in comparision.
But those are just my thoguhts.