Captain Burns. The pressure he generates would make it too hard for Endeavor to touch him and even when he gets close, his strength is much higher. Any flames Endeavor throws at him, he could potentially nullify as well.
Endeavor's flames are fierce and he can shape them as he sees fit.
But Captain Burns' blaze is not only overwhelming, it is also mystical in nature, so there are esoteric factors to account for, that makes him way more lethal.