H&R will be smoother, eibach known to be harsh. Intakes: stillen make cold air intake, i heard it makes growling sound. Or you can go with short ram, such as fujita (the one that i have) makes a turbo kind of sound.
---------- Post added at 02:19 PM ---------- Previous post was at 02:16 PM ----------
and for gas mileage, i never seen a difference, especially if the intake makes a nice sound they want to hear. Most people starting riding their car even harder after the install