What is the most economical small car? I need to downsize from my Mercedes E320. I have children, so need space as well as economy. My heart is set on a Mini Countryman (with up to about 60mpg, allegedly), although I've also looked at the Ford Fiesta and VW Polo. According to real-world feedback at honestjohn.co.uk, the Mini Countryman diesel returns 44.5mpg (or 48.5mpg with two-wheel drive), the Fiesta Econetic 1.6 60.8mpg and the Polo Bluemotion 1.2 64.6mpg. These figures change, however, as more drivers upload their experiences.