We have the same scenario (2 & 2, SNA) and we take a taxi. I think it's $45 + tip and we're at the hotel 25 mins after walking outside. From baggage claim it's about 100 feet to the area where taxis and shuttles pick up at and there is a line of taxis waiting and we're off in 2 mins. We haven't used a shuttle before but with those the times can take longer if you aren't the first drop off point. Plus, if you're the first on a shuttle they may wait until it's full before leaving. I've heard that with shuttles it's usually best to plan to get to your hotel an hour after landing to pad possible wait times.
So, having said that, guess it's what that possible wait time is worth to you. For $45ish you'll be there in 25 mins. You may get lucky and get on a shuttle that's just leaving and be the first drop off and be there in 25 mins for a smaller cost or no cost at all, but just as easily not arrive until an hour after picking up your luggage as well.
If you're not in any hurry a shuttle would be fine but if you need/want to get there quickly a taxi may be the way to go.
I will add that the whole setup of SNA is great. A really easy terminal to get through, picking up luggage is a breeze and it's a straight shot to the tax/shuttle stands. So, you'll definitely appreciate choosing SNA.