Now that employee car benefits and car capital allowances are based on CO2 emissions it is really difficult to compare cars and make any sensible comparisons as to whether to have a company car or take the cash instead.
At a garage I put the data for a variety of car models onto a spreadsheet and found that it is all something of a lottery, because cost, mpg and emissions do not correlate.
However, I did note that if you take capital allowances into consideration it often pays to "go green". If you have a high annual mileage, electrical and dual fuel cars are possibly impractical; most diesels have better mpg.
So, study the models on offer; if you are happy to drive a car with reasonably low CO2 emissions (also checking that it has reasonable fuel efficiency too) then you can have a tax-efficient company car.