Like most of us, you want to reduce the cost of driving. I have own several diesel cars, and enjoyed great fuel mileage (VW rabbit averaged 49 mpg for 120 thousand miles.) However the extra cost of diesel fuel now and the large expense if engine or injection repairs are needed (my VW had to have the cylinder head replaced twice. $400 for parts only both times), would cause me to decline to endorse a diesel (unless you are going to buy a new vehicle every 2 or 3 years or drive about 100 thousand miles a year). I am not in favor of hybrid vehicles yet. The higher initial cost and very high potential repair cost cause me to favor one of the higher mileage rated gasoline cars. The miles per gallon of fuel contributes to the total cost, but not as much as depreciation, upkeep and repair of the diesel or hybrid vehicles. I prefer to buy low mileage (under 80 thousand mile) vehicles about 3 or 4 years old with a carfax report.
