Magic Mountain definitely has the most, the biggest, and the scariest roller coasters.
Knott's Berry Farm (in Buena Park, about 30 mins from LAX) also has several big coasters.
Disneyland has a few, but nothing that goes upside down or is super scary. I am a total wimp when it comes to roller coasters (will NOT go to Magic Mountain) but I ride all the rides at Disneyland because they are pretty tame.
Universal is fun and the CityWalk is there too so you can eat, shop, bowl, etc. But they don't have big scary coasters the way Magic Mountain does.
Just read the other replies... I have to say to skip California Adventure and Legoland. Neither one even comes close to the others you're considering. And maybe my recommendation for Knott's isn't good after seeing what other thrill-seekers say about it! :D