Is there an argument to be made, however, that JMZ's blazing knife palm was also an 'edged' palm-attack and thus he was able to use his own 'edges' to clash against the 6MSJ 'swords'?
Anyhow, as for original question, Xu Zhu without a doubt. Not only does he have access to top-tier techniques, his internal is second to none in all of DGSD. He's the only person in that novel who has been shown to be able to shrug off blows from a XF-caliber opponent a la Jiumozhi. Jiumozhi landed TWO knife-edge palms against Xu Zhu, who shrugged it off while Jiumozhi himself felt his palm hurting. Similarly, when Jiumozhi smashed him on the shoulders with the Vajra Fist, Xu Zhu shrugged it off completely.
The only one who had been proven to be tankier is Shi Potian. No one else!