I don't know anything about the cost of flights from the midwest, but my preferred airports are SNA and LGB (they are both very close) LGB is a very small airport, and SNA is pretty small, but definitely larger than LGB. I don't mind flying into LAX at all, but a lot of people hate it... it is still about an hour from Disneyland.
SNA and LAX both have very low prices for rental cars if you are going to get a car, so that may factor in, but I've also gotten about the same price for cars at LGB by bidding on priceline.