I didn't check the coupon link above, but probably the online coupon code below is a better discount.
If you reserve SuperShuttle online before you go, use coupon code UYR59. Do a separate reservation for each member of your party (even the kids), and you will get $3 off each way ($14 RT per person). Be sure to use the hotel name and not the zip code or the fare quote will be much higher! You can prepay the tip as well. Just be sure to print and take a copy of the receipt with you.
For 4, roundtrip on SS would run you $56 plus tip. A taxi would be roughly $75-80 plus tip.
A taxi is more convenient, but I rarely wait longer for SS than I do for a taxi from SNA airport to the hotel. What I do sometimes is to take the shuttle to the hotel and a taxi back. That way, you can just walk out of the hotel and grab a taxi--no need to call ahead or prebook or anything and no other stops. We stay onsite and get a taxi voucher from Guest Services that gives you a flat rate of $32, which is a good deal!