LAX is a much bigger airport and is definately further away from DL than SNA but there is transportation to DL from both. You'll notice the most difference between the airports on your departure (return to home).
As for traffic, it depends a great deal on when you'll be on the road. Coming from the airport to DL from either airport, you'll experience heavier traffic beginning by 3:00 pm through about 6:00 pm. For your return to the airport, you'll see traffic more in the morning hours starting around 7:00 am through about 9:30 am.
If you're flights put you on the road outside of those windows then you won't have much of a problem from either airport and LAX will only add about 20 minutes. Traffic around LAX during those times though will substantially increase your travel time (by about 45 minutes).
I'm sure others will share their thoughts and experiences.
My personal preference is to save the money and use LAX.
Here is a good tip though. Look at Long Beach airport. That can *SOMETIMES* be cheaper and that airport is small, easy to get in and out of, and is much closer to DL than LAX.