What is your planned method of Disneyland transportation–how are you getting here? If you are flying in for a vacation focused primarily around the Disneyland Resort, it is not hard to rent a car from an agency in Anaheim for a day or two to get out and about; that might be better than renting the whole week and paying for parking when it sits in the nation’s largest parking structure for days on end. Of course, you may get a great weekly deal that makes paying the parking worthwhile, in which case you would have more flexibility.
But for a bit of O.C. ambulation you can take public transportation, rent a cab or get a car for a portion of the week. I would try and settle that well ahead of time, as car rental rates and availability are much better if you reserve in advance.
Driving Yourself Around Disneyland
Before you come, you’ll have printed out directions to your hotel. If you’re driving, you get off Interstate 5 and drive right in. It’s best if you’re not trying to drive through Los Angeles towards Anaheim too late in the afternoon. By around 3 pm the outgoing freeways are often jammed; if so, it’s not the end of the world. Just make like an Angeleno and put up with it. You’ll arrive eventually.
But from 3 to 7 pm is not a great time to be on the freeways (unless you are somehow getting paid for the number of times you hit your brakes). The morning rush hour is from before 7 am to around 9 or 9:30 am. The traffic is worse going into L.A. in the morning, but can also be ugly in the other direction.
Driving in from the east is bad in the morning; you’d be better to stay and have brunch in Victorville (I-15) or Indio (I-10) and drive so that you get into Orange County after 9:30.
Airports Convenient to Disneyland
The best airports are Orange County/John Wayne Airport (the closest, but Ontario and Long Beach are pretty close also), LAX (the most flights), Ontario and Long Beach. Burbank Airport can work also, but not quite as convenient. There are good shuttles to the Anaheim area from all of these airports.
I’d not pick San Diego/Lindbergh Field as a great choice for Disneyland transportation, but there definitely are halfway reasonable ways to do it if that’s what seems to work best for you.
Travel by Train
There is an AMTRAK station within blocks of Disneyland; this station also serves the regional Metrolink rail system. (You can later use that station if you want to jump on Metrolink and go up to Los Angeles or down to Mission San Juan Capistrano for part of a day.)