I like my 4 dr - easier with the kiddies for sure. It's mechanically very similar to the is - I think the differential has slightly taller gears and the anti-roll bars are thinner in the 4 dr, but that's about it. The 2 dr has sport seats, a rear spoiler, and weighs very slightly less. Of course, the bars, diff, and seats can be fitted to a 4 dr easily. My 4dr came with a ltd slip diff, fogs, and an is front lip along with fat tires on light-ish wheels and a chip, so I'd bet it'll stay with a stock 2 dr pretty easily. I'm planning on upgrading bars soon, too. Currently I'm at ~27 mpg in mixed driving. Others claim 30+.