Disneyland and California Adventure together will give you most of what you'll get at the entire WDW resort, with several plussed attraction (Pirates, Indy, Space) to boot. WDW won't offer you much aside from the far superior Tower of Terror, slightly superior Haunted Mansion, Everest, and Rock n Rollercoaster. The latter two don't compare to Universal's coasters anyway, imo. And you're going to have to navigate all four parks to see everything. Universal's parks are within five minutes walking distance from each other and if you stay onsite you get a free water taxi to and from the parks, and an express pass which acts like an unlimited Disney fastpass with no time restrictions. Highly recommended.
I'd also recommend Universal for Spider-Man and Forbidden Journey, which you can't get in California (also my number 2 and 3 rides in the world behind Transformers), along with the vastly superior Mummy (my number 4) And that's not even considering Gringotts next year which seems like it will render damn near every other dark ride in the world completely obsolete.