Disneyland is compact. There is so much to do in only 85 acres. My local Six Flags amusement park is bigger than Disneyland, but you would never know it from the number of activities you can do between the two of them. Then you have Disney California Adventure right next door and Downtown Disney right next to both. I believe it's still true that there are more attractions at the Disneyland Resort than in all of Walt Disney World (doing a quick Internet search, there are about 53 attractions at Disneyland itself and about 56 in all of Walt Disney World, although the definition of attraction varies).

Walt Disney World is so much more spacious. Magic Kingdom itself is just so much bigger, and thus it doesn't feel as crowded. They have room for all sorts of different types of hotel resorts, have an animal park, and the uniqueness that is EPCOT (I wish Westcot had happened).

To me, it's like asking which is better, cinnamon rolls or chocolate cake. I love them both, and they both serve a similar function, they're great in their own ways.