I already saw Kill Bill... So I'd prefer to see Boondock Saints 2, seeing as how they're supposed to be two different movies.
Last time I checked, Kill Bill had a female protagonist, who was an assassin, wielded a katana, and was on a revenge mission to kill the man that left her for dead at their wedding.
Boondock Saints II is about two brothers, with guns, who are out to clear their name because someone is impersonating them.