Whatever you buy get the biggest engine option! I know it sounds crazy, but when you look at the weight to power ratio gas millage will stay about the same(unless your talking something with a v-10). I will use a ford explorer as an example they had 3 engine options 1 v-8 and 2 v-6's (5.0, 4.0, 3.0) the 3.0 and 4.0 due to the lack of power get the same milage in realworld conditions as the 5.0. Same goes for trucks,vans, and larger suv's.