I used to have a thousand as a car allowance. When you factor in that this also has to cover insurance (and often anything other than gas) 1000 is not all that much. When we were taken over, the new plan was 650 so I chose to have the company car instead. Don't forget the 1000 is also going to be a taxable benefit.
So really 1000 is not that much.
take taxes of 300 or so
that leaves 500-600 for a car. Which is not that nice a car once you factor in taxes etc...
If you do get an allowance then it will normally cover maintenance as well...typically only gas is then covered.
For these reason I prefer having a company car. You get the car. Insurance is provided. No expense what so ever for the business portion. You will get a tax hit for the portion you drive for personal.
Oh and do read fine print. Many companies are moving to an emission conscious mindset meaning that the allowance is cut significantly if the car (which you ar driving) is older than 4 or 5 years.