The Roku Streaming Stick is an oddity among Roku's range because if you're buying it separately, it's because you own one specific TV: the Insignia E480 television. While some other TVs do have the necessary MHL port, the Insignia TV is the only device that supports the Roku Streaming Stick that doesn't already come with one. As a result, the Roku Streaming Stick is currently a very niche device; get one of the other Roku devices instead.
While we hear there are more MHL TVs coming at CES, it's likely that these TVs will already include a smart TV suite. Even if you still want to get a Roku to maximize your streaming options for compatibility's sake you're safer with a Roku HD.