Lets be real, soccer if you are here in the US. But for the rest of the world..... FOOTBALL! Futebol! futbol!
Yes, definitely football, unless you have a website with a huge bias towards the USA. Having said that, I thoroughly enjoy playing the football management game over at SoccerManager.com.
As most people are saying - it depends on your target audience. What is the subject of your blog? Football/soccer is a huge niche. Are you planning on writing about the game itself? If so, from what perspective and focussing on which country/league? Or, are you planning your blog to be about merchandising? Selling equipment, etc? As well as 'football' or 'soccer' you shoud also be asking what domain extension is best. For example, if you are going to be targetting a UK audience and be writing about the Premier League a .co.uk extension may well be preferable to a .com, whereas if you are targetting US traffic then a .com is the way to go. Finally, what is the 'level' of the writing? Again, comparing the US and UK, you will find, in general, that UK readers are much more knowledgable and have a vastly different perspective on the game to Americans. Football coverage in the UK (and Europe) is extremely in depth and you should think carefully about your target audience and what unique things you can offer them. Hope this helps. Rob