We always take a taxi from SNA and it costs around $30.00 to the DLH or GCA, which for us seems to work out cheaper then the shuttle.....plus you go directly to your hotel and not to five other places to drop people off.
The taxis are always ready to go as we walk out and then available when we are ready to go back to SNA.
We have used Supershuttle and it is fine. However, if you have 3 or more people, it is the same cost to take a taxi and then you don't make any stops! If you have 4 or more, you might want to look into towncars and/or limos. You can go to limos.com and get 10-12 quotes. Depending on how many in your party, it might be worth it.
I have used the http://www.airportbus.com service. Most of the time it is fairly good, but one time we were waiting for it and it never came! we had to flag down some tacky "Mickey" This, or "Disney that. but we got there. I am sure if you call Airport shuttle you will be fine