Answer based on OU and Natdex OU, as well as performance during playthroughs.
Bisharp and Kingambit are both much better when used offensively, which means their damage output matters more than their bulk. In UU, where Bisharp is viable, max physical attack Bisharp is much more common than Bisharp with any significant amount of defense EVs. This is despite the fact that they almost always hold eviolite. source Kingambit has a more reliable ability and higher physical attack, which means it's much better at being an offensive tank than Bisharp. Eviolite Bisharp has lower base HP and defense stats and can't hold leftovers, so it's effectively only a little bulkier than Kingambit.
252+ Atk Bisharp Iron Head vs. 0 HP / 0 Def Dragonite: 145-172 (44.8 - 53.2%) -- 31.6% chance to 2HKO 252+ Atk Supreme Overlord 3 allies fainted Kingambit Kowtow Cleave vs. 0 HP / 0 Def Dragonite: 214-253 (66.2 - 78.3%) -- guaranteed 2HKO
source The Smogon nerds also ranked Kingambit above Bisharp. source