I've had both f30 and e90 328i loaners. I can say that I enjoyed the f30 much more more than the e90. Engine feels more peppy due torque with the FI.
As for gas mileage, I think there was something wrong with my loaner. When I picked it up, the average MPG was 24+. After 2 days of driving, it is as below. You think I should take it back and ask them what is wrong with it?