Baseball and Soccer are basically tied for most boring. I would even rather watch golf but it is a close 2nd to the other 2. Baseball and football are both boring to play and watch, except for the few exciting plays in a game, it is 3-4 hours of long boring nothing interspersed with the occasional exciting play. You know it's boring if you can see literally every single exciting play in a 90 second spot on sports center. Golf is really just meh, although I play golf so I can appreciate the complexities you just don't get if you don't play. But it isn't very much fun to watch overall. I could never stand soccer long enough to watch more than a couple of minutes of it and playing it is brutally boring. So I guess for me in order of most boring to least boring it would be:
1a. Baseball
1b. Soccer
2. Golf
3. Football
I don't consider nascar to be a sport at all.
Basketball is obviously the most exciting sport to both play and watch. Rarely a dull moment, unless a team is down 3-5 points in the final minute, in which case you better plan on 30 minutes of hack-a-whoever followed by free throws. But even then there is the chance of a last-second shot that amps up the excitement level.