For me, if I the subject 'gets' me, I build it. Period. Sure, I have my likes and dislikes, and there are certain genres and car manufacurers I favor above all others, but if I see something I like, I'll get to modeling it eventually. Sometimes I'll even buy a kit of a subject I'm not too wild about just to see what all the fuss over it is about, and oftentimes, I'll build that kit in accordance with my tastes.
And this doesn't just apply to auto models- I've built everything from a Batman Batwing, WWII battleships, a Star Trek model or two, and a Ford Tri-Motor plane.