IDK how to hide spoiler comments on mobile so I you’re someone reading this who doesn’t wanna be spoiled stop reading.

Well since all the Original 13 Longinus work differently it’s hard to say exactly who’d be the strongest. As well as are we going by just having the Longinus or their other powers as well. Cause issei who if he mastered full force of ddraigs power in cardinal crimson, masters the max power of ophis he can take, and finally use great red’s power he’d definitely be at the top but my guess is he’s not getting that far until maybe mid way of dxd Shin. Same with Vali- I think he has almost full control over albinos power in empiro form but I’m not sure but similar to issei if he masters full power of Albion, ophis, and further perfects his Lucifer power he won’t be as strong as whatever isseis new form will be but if he’s lucky may get onto level as great red or ophis maybe even higher. If we are just going regular human Longinus I’d say it’s between Cao Cao or Tobin Ikuse. I’d lean more to tobio tho because in the end Cao Cao’s spear has a change of failing him if the truth idea doesn’t work. And considering tobio has full mastery of his cainis lyakon. But it all depends on their training. While Cao Cao was able to beat up on issei in volume 12 for majority of the fight while issei was cardinal crimson and Cao Cao was in Balance Breaker it He wasn’t ultimately stronger than issei to the point where it wasn’t even a problem. So I’d honestly say he taps out at Longinus level right above god and that’s about it. But if he fully mastered his powers and went against tobio id say it’d be the strongest battle between the strongest human Longinus. But in the end if issei and vali mastered their gears + ophis power + Great Red/Lucifer Powers Cao Cao and Tobio wouldn’t stand a chance against these two.