Courier Six? Survived two gunshots to the head at point-blank range, seems to be experienced with walking long, hard and dangerous roads according to Ulysses, robbed the Sierra Madre blind while a bomb collar was strapped to his neck, out-foxed the guy who put it on him and lived to tell the tale, is one of the only four people to survive the Big Empty, walked the Divide and lived to tell the tale (only two have done this), assassinated OR prevented the assassination of NCRs President, prevented nukes from being fired on the NCR and Legion OR did so himself, and single-handedly secured the future of the Mojave as what it is (what that is, we don't yet know) for generations.
Ulysses? Again, survived the Big Empty, worked as one of Caesar's best scouts and Frumentarii, responsible for the fall of New Canaan, one of the only two people to walk the Divide and live to tell the tale, had the willpower and the conviction to threaten a nation with nuclear weapons.
Graham? The First Legate, led Caesar's army for a time, feared by many for his mercilessness in the face of his enemies, both those captured and those being fought, survived being lit on fire and thrown into the Grand Canyon, survived multiple sniper shots to the head.
Vulpes? Lanius? Elijah? Christine?
Soooo many badasses have walked the Mojave. Who do you consider to be the MOST badass?