There are different types of shuttles.
For SNA airport
We tried the "walk up" shuttle run by the taxi company. As we walked up, the only other person in the shuttle got out and was complaining about the wait. We sat in the shuttle for about 2-3 minutes when I realized that the shuttle wasn't going to leave until it was full. We got out and I asked when the shuttle would leave, and I was told 5 minutes. This just confirmed for me that they needed more people and the 5 minutes was just a hook to keep me.
Then they didn't want to give me my suitcases. So I had to open the rear door on the van and get them myself. The whole time they kept trying to convince me to use their shuttle. At that exact moment the
Disneyland Bus showed up and we hopped on and it left immediately
For 2 people the Disneyland Bus is cheaper, for 3 or more a Taxi is cheaper. But after my daugher got sick in the middle of the night and we had to wait for a Taxi, now we rent a car.
If you use priceline for a rental car, be sure and get a receipt for the gas when you fill it up. The car rental agent tried to charge me for gas based on the mileage we drove, until I showed a gas receipt. It seems they don't use the gas gauge of the car to determine if you put gas in it. This has never happened when I rented directly from the car rental companies.