Personally I like 'em both, but for vastly different reasons.
F1 = the top technology, the most exciting circuits, and soap operas that are more compelling than anything on TV!! Plus, NOTHING sounds like an F1 engine.
NASCAR = Competition, competition, competition. MANY more than 2 or three drivers have a chance to win a given race. F1 is vitually devoid of competition. I wouldn't be surprised to see Alonso win every race remaining this year. The only lead change at Silverstone happened because of a pit stop....YAWN