You don't get much more badass than this. Girl Genius just keeps getting better & better.
Dresden Codak may operate at a higher artistic level, but it's also a once-a-month sort of operation, and is almost openly hostile to linear narrative. The Foglios crank out three color pages a week like atomic clockwork, with an exceptional narrative flow. Order of the Stick has a similar fidelity to strong, well-written narrative, but Burlew's art style is just less demanding than the Foglios', and he's not nearly as reliable, albeit not bad by online standards; also, the fake-RPG story and subcreation is clever but doesn't even pretend to originality.
Perhaps the closest competitor to Girl Genius is Howard Tayler's Schlock Mercenary, which has long since outgrown its original crap art & comic-sociopathy humor for a polished style & intricate space-opera plotting. But in the end, Schlock Mercenary is a *strip*, while Girl Genius is a graphic-novel serial. The Foglios are operating under a different and more demanding set of artistic constraints than Tayler. Also? Schlock Mercenary is a comedy which pulled a Cerebus, while Girl Genius has always been a serious story with a wide streak of comedic relief-style humor.