As Goofyfordisney says, use John Wayne airport. If traffic is good (do not drive in LA/Orange Counties between 6-9am and 3-7pm, unless you love traffic) John Wayne is 20-30 minutes from DL.
The Closest is John Wayne (SNA), but many also choose to use Long Beach - Very quiet. Not crowded at all...of course not many flights either, but no crowds.
~Tina