In L.A. terms, LAX and Burbank are roughly equidistant from DLR. This may not seem true looking at a map, but timewise it'll be about the same drive. In fact, I'd prefer the drive from LAX to DLR, using the 105 (DO NOT use the 405) to the 605 to either the 5 or 91. Much simpler than it sounds and much, much easier than any other route.
If you can fly into Long Beach, that's ideal. Otherwise, Ontario is a terrific option, but it's a long drive to DLR. OC Airport is very close, but usually more expensive. LAX is good. Burbank is almost always pricier and the drive down on the 5 can be nasty at certain times.