Generally, Mileage is the easiest way and the IRS usually allows a pretty fair mileage rate (I think it's around 50-55 cents per mile in recent years)
However, if you purchase a new car you will probably want to do itemized deductions for 5 years as you can write off the depreciation of the new car.
It's a sliding scale where the biggest writeoff is the first full year that you own the car, and then it declines each year for 5 years until the car has been fully depreciated.(the tables with the %s are in the tax instruction booklet)
I'm in the middle of doing this right now. I purchased a new vehicle in June of 2013. So for 2014 my deduction wasn't huge, as I only owned the vehicle half the year of 2013. This past tax filing was where I had the BIG deduction, as I owned the vehicle for the entirety of 2014. I think I was able to write off something like 38% of the full vehicle sales price (adjusted then for the % of business usage, which mine was about 55% business use, 45% personal use), so the actual deduction was purchase price x .38 x .55 for the year, so it was a nearly $6000 deduction(plus doing itemized deductions you can add in all other expenses such as gas, oil changes, etc) so this year I definitely benefitted from going itemized + depreciation over just a flat mileage-based deduction.