Most fun to watch would have to be the Rays, Blue Jays, Cardinals, and Reds. The reason for the Reds and the Cardinals is because of the back and forth divsion lead. The Rays and Jays because of how they stack up to the Yankees and the Blue Jays, which both of them are doing very well this year.
By far, the most boring team to watch would be the Pirates, Orioles, or the Astros. They are all horrible teams but have nice ballparks.