As an American who grew up on baseball/football/basketball, soccer is a taste I've acquired since I started living in Europe. It took some time for me to develop an interest, but since that happened, I have to say there is no contest: soccer is more exciting than any of the major American sports.
This is not entirely or even mostly due to innate interesting-ness or exciting-ness or whatever (basically seeing any of these sports played at a high level can be pretty exciting as long as you are reasonably informed of the rules and understand the game and so on), but rather due to the fact that American tv advertising cannibalizes its sporting events to the point that they become almost unwatchable at times.
American football is currently the most popular sport in the US and would probably be deemed by many as a model for excitement. LoL? Not that football can't be exciting, but watching an NFL game is like watching three hours of commercials with occasional game breaks that largely involve people standing in a huddle.
Soccer is boring because the ball spends a certain amount of time in the mid-field while each team tries to find ways to break down the other? Basically it's commerical + huddle time, but 10x better. A soccer game that lasts 90 min can reliably be watched in two hours approximately. A 60 minute American football game can take three hours to actually complete.
Basketball? Occasionally an NBA game can be watchable if there aren't too many fouls called, at least until the last few minutes if the game is close, at which time it will grind to a halt as the teams call timeout after timeout so that 30 seconds takes half an hour (including commerical breaks, of course).
Baseball? My favorite American team sport traditionally, at least it keeps a basic rhythm of sorts, despite commercials, due to the inning structure. Though once you start getting into multiple pitching changes, oh man can it start to drag. And it is a game where not much happens a lot of the time to begin with.
Obviously opinions is opinions is opinions, so take it for what it's worth, but my feeling is that soccer makes for a better spectator sport than any of the popular American sports as currently presented. It would be a closer contest if you just got to watch the fucking game

, as with soccer.