In all the times I've used a car/limo service, I've only once had a bad driver. That was with Florida Towncar Company, who I'm not sure is even in business any longer.
For the past four years I've exclusively used Jim Kropp from Golden Limo who is now with Lorden Transportation--Dennis with Lorden is wonderful as well. I've never had a reason to give him less than 20%.
I always had good drivers with Tiffany Towncar, and it was only the snarly office chick that made me stop using them. I also formerly used Yoour Ride back when Rabbit owned them, and stopped using them after he sold the company because the new owners drove it into the ground.
I would much rather book a car service or limo company based on recommendations from people on these boards who do'nt have a vested interest in the company, which is one of the reasons I take Edd's posts with a grain of salt--although I do agree, if you get a bad driver, adjust the tip accordingly.
Anne