I played football/soccer for a few years when I was younger, and I enjoy watching the World Cup, but overall, it doesn't intrigue me all that much.
American football, however, I love. Though I only played it for a year (I quit it to play basketball, which I recently quit to play tennis lol), I've been watching it all my life. I'm not too big a fan of the NFL, but during the college football season I watch 3 games per day on average, and I spectate at all my high school's home games and a few away games, as well.
There's just an ineffable excitement that American football carries that I've never experienced with football/soccer, which makes it the clear winner for me.