First, I think everyone knows how I feel about Star Wars....
In any case, this argument is doomed. Han Solo isn't even the coolest or most bad ass character in his own series of movies, let alone overall.
R2-D2 is clearly and without a doubt cooler and way, way more bad ass than Han Solo.
Evidence: EVERYTHING R2-D2 does in the entire series.
Other characters that are way more bad ass include: Tony Stark, James Bond, and Steve D.