When it comes to series, I prefer Formula One over everything else. But I like all types of racing and rallying. My uncle bought me a toy formula type car when I was a small child and I've been fascinated by cars and racing ever since. Of the various series within NASCAR, I prefer the truck series over Sprint Cup and Nationwide. But on occasion, I'll watch all of them... especially when they race on the road courses. Road courses, IMO, offer the best test of skill and endurance. And one thing that is unique to NASCAR (and other stock car series) is the short track. If you have a chance to go to only one stock car race, make sure it's a short track and I think you'll have the time of your life.
I used to be a huge NFL and NBA fan. The L.A. Rams was my team and Dr. J. was The Man. But things changed and my taste for stick & ball games (or "sports") waned as strikes, greed, bad behavior and more guys show-boating (instead of being team players) took over. The true "love of sport" is still something that you see in auto racing. It's not across the board. But unlike in most stick & ball sports, in auto racing you'll still find guys who'll (literally) sell the shirt off their backs just to get in a race car one more time. I like that.