For me, first place goes to rally car racing. I don't think there exists any better drivers than those guys. I never have as much fun watching any other race competition than rally car racing, except probably Le Mans or drag racing. The thing is, I hardly ever see much rcr on TV, always NASCAR.....
I guess that's supposed to be the "American" or maybe just southern American icon of racing....
Consequently, the most boring racing to me is probably NASCAR, uggghh, going around a big oval all day long is not all that exciting or fun. I do respect those guys for their skill, to be riding at 200 mph and still control the car and bring it under submission if it does a 180 degree spin b/c it got tapped in the rear by the trailing car (like I saw happen a couple of weeks ago). All in all, it's still racing so it's kinda cool, just can't watch it for more than 15 minutes at a time.