I had a company car for 2 years and have switched back to allowance when I changed jobs. BIK is calculated on the original market value of the car, so obviously, the bigger and better the car, the more BIK you pay. Personally I'm better off with allowance, but a lot depends on mileage, amount of time in/out of the office etc.
When I bought my own car earlier this year, only FBD and one other insurance co (can't remember which one) gave me NCB for my claim free driving on company policy.