In this list, utilitarian means that the vehicle is ugly because function was the primary design goal, with æsthetics falling by the wayside. Military and farm vehicles are the main contenders for this category.
Ugly applies to vehicles that imitate the form, but not the function, of utilitarian vehicles. The VW Type 181 (also known as the Thing) is the best example of this category. It is a clear descendant of a German WWII military vehicle, the Type 82 Kubelwagen, but has none of the functions associated with off-road or military use. Well, it does take over 20 seconds to get from 0 to 60mph (40+ seconds for 0-70), and the interior noise level is 90dB at 70mph, so it's in the Hummer league in at least two categories.
Lima-bean shaped vehicles need not apply. For this list, the more angular and the more flat panels of sheet metal used, the better.