Easy Valley here, so about 6 or 6.5 hours driving depending on how many stops we make for bathroom/food. It's a hot boring drive across the desert, but it's all interstate. When my kids were little it was a tougher drive, but I still felt better if they cried/misbehaved in our car than in an airport or on the flight.
I have flown to DLR when it was just me, but if two or more people go, I think the airline cost is always going to be higher to save barely a couple hours. Plus people have pointed out the ability to bring a cooler and all your stuff -- we eat all of our breakfasts in room and that saves us a lot of time and money too.
If you are going anywhere but DLR while visiting SoCal, you're gonna want a car, so I'd rather bring my own.
BrienBear pointed out that even airline employees sometimes drive -- my sister and her family often did that when my BIL worked for US Airways. The stress of getting 5 standby seats on the same flight, combined with the rental van cost once they got there, meant they really didn't save any time or money.
PHXscuba