dude, rly seriously, the lee sin wins both in a blind duel (moving foward and using all you have), and on a skilled lanning, first i want to say that for some reason the darius ad is way too high, because, his base damage at level 18 is 113 (same as lee), and if they use same runes/masteries/items, that 499 on darius can only be wrong (he has no ability that raises his ad), and armor on darius is also wrong, you gave him 4 quintences, and... there can only be 3, but anyway, if you analyze their skills on a blind duel, lee sin's q is same damage as his q (i mean lee sin's q-q), proceeding, the w from darius is a low cooldown 200% damage, thats pretty nice, i mean like 1 crit each 3 secs (their as is basically 1/s so 1 crit each 3 secs), on that hand, i think you also is on the edge lee sin's w, his w shields 200 damage, but gives a lifesteal buff (that will compensate the damage not shielded), keeping on, lee sin's e vs his e: the e from lee sin damages for 200, and gives you up to 60% AS slow, and all that darius e does is pull, and also gives armor pen, but on this whole e, lee wins, so next 2: ulti and passive: passive: if well played and regulated, lee sin haves a permanent 40% bonus AS for all the duel long, darius passive is do 36 dps, and i just think that with so high AD from both, 40% bonus AS > 36 dps, and for the last, ULTI! lets see: max damage from darius ulti (counting on 5 stacks of bleed): (680 base + more 1.5*455 = ~680 from ad scaling WOW = 1360)
...
ok...
lee sin's: (600 base damage + 2*455 = 910 all = 1510 WOW)
anyway:
i don't want to get kicked by any of those, but, the darius has true, and lee's normal, so darius ult kinda is better, counting on that they have some armor, but the ult is gonna be used once, and by the long of the fight, lee sin will have more damage, that soon will overhelm darius before he ults, and i didnt even said about lee's 8% lost health scaling damage kk, anyway, on a blind duel, lee sin wins.

But about on a more strategic fighting:
lee haves more mobility, no mallet or slow can stop him from jumping on everything, so he could probably dogde most of the harass, and he also can get in and out very very quickly, so he will harass, and darius can't chase... and, if darius try to run, he is gonna die, because he has no scaping mechanisms, and lee got 2 dashes only on skills, so, if darius stays, he makes damage, but when lee dicides, he will die, if he try to run, lee chases him, and he dies...

so, basically: (counting on this build)

LEE SIN > DARIUS

*before saying: but darius is dah best! read all what i've typed