I tend to run a mixed selection of vehicles. I like trucks as they fit into tighter terrain than my battlewagons. Plus mine look like hot rods, so that's a reason. And they go fast, my Evil Sunz like that too.
In short Iike them for themeatic reasons. I actually don't like GWs Trukk model, too big, too expensive, but the bits are great to build something more appropriate.