We used Starz, and I don't recommend them. We had some issues. Nothing that like, wrecked the experience, but it was less than stellar. It was still very nice to get picked up at the airport and driven directly to the hotel; there was soda for the kids and champagne for us, fancy lights that changed color on the ceiling, and people staring at us on the freeway, wondering if we were rock stars, behind that tinted glass.

Very fun!
However, I love the idea, and you are going to love the reaction you get! I did it as a surprise for my family's first trip. It was so freakin' FUN to see their faces when that limo pulled up. DH had flown into SNA for business often before, and he thought we were getting Super Shuttle. Here's how the conversation went:
Me: Ok, wait right here.
DH: We have to cross to the center island to catch the shuttles.
Me: No, we're fine right here.
DH: (looks at me like I'm crazy, but he knows better than to argue with me, so stays silent for a tense couple of minutes)
DH: (finally says urgently) Really, I'm telling you, the shuttles go from over there...
Me: (seeing the limo coming)No, really, I'm sure we are fine right here.
DH: (is thinking, "humor her, she's nuts but I have to sleep with her so I'll keep my mouth shut till she realizes her mistake...")
The limo pulls up, the driver jumps out smartly and introduces herself and opens the trunk and starts piling our luggage in...
The kids go WOO HOO and DH is standing on the curb with his mouth hanging open...

It was so priceless!