Popular how?
To play in amateur recreation? Well then I'd say cricket, football is too expensive to casually play and is thus confined to a smaller audience (mostly America)
To watch as a fan? Well if we're just talking sheer numbers of viewers I'm not so sure. Sure, Cricket has a wider audience, but Football has a richer audience (more viewers that can actually afford TVs and electricity). Evidence suggests the superbowl as a clear winner in sheer number of viewers, but the vast majority of the viewers come from America.
To invest in as a fan? Well then the obvious answer is football.
http://sports.espn.go.com/espn/news/story?id=2749584
But the key to the question is
worldwide. Just because the football's American audience makes it this huge juggernaut doesn't mean the rest of the world buys into it as well.