I had a full size mx7000 and took it off for gas mileage, and to go undercover. that being said, i went back to a bar on top for 2 reasons. 1, i hate fighting traffic with horrible intersection coverage, and 2, i found a sweet deal on the mini-liberty i have now.
for those with long commutes, or drive a lot on the highway, it will deffinately benefit you in the long run to go slick top. a nice interior bar can go a long way.