We've used Go Lansky 2x. First time was awesome experience (with 1 2 1/2 year old) car seat & installation were fine. We loved our driver for that trip.
Second time (3 1/2 year old & a 4 month old) was awful - different driver and they provided expired car seats & had no clue how to install them (both directions - from & to the airport). No need to mommy guilt me here, I've already beat myself up about this enough.
If using a car service & traveling with young children I would either bring your own car seat that you are familiar with the installation or use the Disney Bus ran by Grey Line.
If you're not traveling with children requiring car seats, then I would totally use them again.
(Side note, after contacting the owner after our last trip in November 2014 he did say he went out and bought new car seats, however I still wouldn't use them again bc I am not confident that all the drivers are know how to install them properly).