I would rent from LAX over SNA any day of the week... Selection is vastly superior and they actually use their ER sections. SNA is a hole with small EA/ES and the rest being bulk storage. I also see minivans on EA/ES frequently at LAX and did not see any at SNA (though they did have a Pathfinder 7-passenger SUV).
That said, check the rate for a Minivan at Disneyland location... Without the airport fees/taxes it might not be much more than ICAR at SNA or LAX.