I enjoy keeping my vehicle dirty on the outside so people can tell that the offroad tires arent for nothing..
Today I washed my 4runner and BOY does it look good clean.
What do you prefer and why?
Clean, though I'm not obsessive about it. For me it's just to protect the paint. I mean, trail damage is trail damage (ie trail 'pin-striping' is ok, and I have a lot of it), but if you neglect your vehicle you will only hasten the deterioration of the paint, leading to other issues like rust. Keep in mind, the paint on your exterior is not just for looks.
IMO, driving around with mud on your rig from a trip you took weeks ago is kind of a poser move.. :p Either that, or it's evidence you don't respect or take care of your gear. :)
Anyone who looks closely at my Jeep (and understands these things) will know it's used offroad. Look at the tire sidewalls (I don't use the shiny stuff on it), the 'pinstriping', the wheel lips, the tailpipe even! lol