I think the mode of transportation best for your party depends a bit on how many in your party, where you are staying, your timing coming in and out of the airport, and how long you are staying.
For 1 or 2 and perhaps 3, the cost of a limo or taxi is probably not worth the cost. Similarly for a rental car, especially if you are staying several days and are not planning on going anywhere besides DLR. For larger parties, rentals, taxis and/or limos are worthy of consideration.
When I fly, I usually travel with just one other person, so we have almost always taken the airporter or a shuttle. Based on my experience with both, I think the shuttle is worth the extra money. Furthermore, I will always fly into Orange Co. unless flights to LAX are significantly less. (In other words, there are more issues with the transportation from LAX than from John Wayne). I've had some long waits for the Airporter bus, long stops in Buena Park (I don't know if they still do that), and uncomfortable buses with broken windows. I've had some decent buses too, but somehow I remember the cold and dingy ones more. With the Airporter, you also may have to switch buses to get to your hotel. With the Supershuttle, there is a risk that you will be the last of 4 or so stops. Only once was this much of a problem for me; they delivered a party to a location that was a bit out of the way. There's rarely much of a wait at LAX for a Shuttle since they usually fill up pretty fast, and the Shuttles schedule your pickup back to the airport based upon your flight time. Shuttles have always picked me up on time for my return trip to the airport. Once I thought Supershuttle had scheduled an awfully early pickup for my returned flight, but I guess they knew what they were doing. We were flying Southwest, and lines at LAX for SW were huge! All in all, I've been pretty happy with Supershuttle.
Seems to me the travel time on Supershuttle to and From LAX was around an hour allowing for an average of a couple of additional pickups/dropoffs. It was definitely longer on the Airporter with the stop in Buena Park. It'd say a good 1 1/2 hours. Those numbers don't include the wait time for the bus or shuttle. Times can be longer during rush hour, but both are able to use commuter lanes.