Advantages of John Wayne:
1. Much closer
2. More compact and easier to get around
3. Shorter lines, sometimes much shorter lines (esp. for Southwest)
4. Much closer (bares repeating) and that means less traffic and time to the parks
5. Cheaper to get to the park or hotel via bus, shuttle, taxi (since it's -- did I mention -- much closer)
6. I'm thinking there is less of a chance for flight delays there; I've had holdups flying into LAX - had to circle or wait on the tarmac for a gate to open up. I've never had any delays in or out of SNA (John Wayne)
7. Less chance of threats that could close a terminal down for a couple of hours (OK, so I'm starting to stretch here).
Advantages to LAX
1. Sometimes the fares are lower in and out of LAX
2. Better people watching since there are many many people there
3. I'm pretty sure there are more restaurant and shop choices if your plane is delayed a few hours.
4. No pesky noise ordinance thing; it's never bothered me at SNA, but has some people.
Unless the fares are much much cheaper, I always fly into SNA. Depending upon your city and airline, if its an option, I understand that Long Beach is the second best option.