J.D. Power survey determines quality improved for 21 of 33 auto brands.
Worst-performing brands were Fiat, Smart, Chrysler, Subaru and Jeep.
Fiat was the worst performing brand, with 273 problems per 100 vehicles.
Cars sold in the US likely would come in at the bottom segment of the market: IHS
J.D. Power cites Lexus made in Cambridge for fewest defects.