The selection of cities is excellent too: Rio, Chicago, Madrid, and Tokyo.
Convenient as it would be if the Olympics went to Chicago, I think language rules it out. Would the Olympic committee grant the Summer Olympics to two English-speaking countries in a row? (Additionally, Vancouver has the Winter games in 2010.)
Madrid, similarly, is probably out of the running by virtue of geography.
Between Tokyo and Rio, I hope Rio gets it. First, Tokyo’s already had the games. Second, the games have never been further south than Mexico City, except for a couple in Australia which hardly count. Third, Rio sounds like a really cool city and the Olympics would be a great excuse to visit.