Whatever you choose, get one with a retention strap, or some positive retention device (Serpa, etc).
In a crash, the gun will go flying out of the holster. Many people don't think just how many G's are exerted on an item in a car crash. Even a minor one as low as 35MPH will create enough G forces to dislodge a gun from some holster designs. Ever hit the brakes with a Big Mac, or bottle of water on the seat next to you?
This creates a "secondary missile hazard". The gun goes flying around in a crash, especially a rollover, and can easily kill an occupant.
Just as importantly, you won't be able to find the gun if you need it after a crash. Like, if you're forced off the road.
IIRC at least one of the FBI agents was disarmed this way in the Miami shootout. He put his gun under his thigh so it would be handy, and in the ensuing crash it flew out and was lost. He had to resort to a BUG.
For a car holster, go with positive retention.