I've used both Karmel Shuttle and Super Shuttle in the past, for different reasons.
I'm not sure how they figure 4 people to a sedan and 3 to a minivan, but just to put a plug in for Super Shuttle - I used Super Shuttle this past December for a "point to point" pick-up - meaning they were coming to my home, getting me, taking me directly to the GCH, and there was no airport pick-up involved. And the gratuity was added into the price. It was really, really costly (over $100 for only one way, and I live in the Beverly Hills area), but I liked the service. They quoted me one rate at first, but then, when they assigned me to one of the ExecuCar/Express Shuttle vehicles, the price dropped by about $24, which was good. The vehicle that arrived was what the cheapest option was, which turned out to be a minivan of sorts.
Anyway, they were prompt - a bit early, actually - and it took 40 minutes to get to the GCH from my house. (It was 5:45 a.m. when they picked me up so there was no traffic on the road yet!)
By the way, the driver I had for Super Shuttle/ExecuCar/Express Shuttle last year gave me some of his business cards. He said that if I needed to do a point-to-point pick-up again, he would do it for a much cheaper price. I guess he has a "side business" shuttling people around. He wanted me to give his number out to anyone who needs a service like that (I told him about the DIS), but I tend to think that people are wary about using a service that they have never heard of before. I've been tempted to call this driver myself and take advantage of the low rate he offered me, but haven't quite brought myself to do it yet. I guess I'm a little wary of drivers with "side businesses" also!!