Sonic is cool because his games revolutionized platformers. It was a platformer that played entirely different than anything else, with level design that rewarded both speed runs and exploration.(particuarly S3&K). As far as a character...Sonic's impatient but very heroic. It's not like he's only attitude. Really, when it comes to his games now...he's a thrillseeker that always helps his friends when they need him. If you think the attitude made Sonic cool, study the 16-bit era. Look at all the bad platformers mimicing Sonic's style without the exceleent level design or intuitive controls. And yes, attitude stretched to the level or annoying. Bubsy, anyone?
Sonic's character is probably more...negative than most company mascots. He's kind of arrogant and self-absorbed. I'm a huge Sonic fan and even enjoy the 3D games, but really the awnser is "Play the games".Mario would just be an annoying character if the games played like Gex.