With most makes, manuals tend to get slightly better gas mileage and BMW is no different. For the '04 325i, both the 5-speed stick and 5-speed steptronic get 20 mpg in the city, while the stick gets 29 mpg on the highway and the steptronic gets 28 mpg. For the 330i, again both stick and steptronic get 20 mpg in the city; the 6-speed stick gets 30 mpg, while the 5-speed steptronic gets 28 mpg. Both of the xi models get slightly worse gas mileage than their rear-wheel drive cousins. I didn't find any data on the SMG.
