with conqueror is max damage
with hail of blades is max burst
or 
with conqueror is probably the most optimal
or 
lethal tempo is probably the best 'tank' build
with PTA as a top build
with DH or Electrocute is fun too
with Dark Harvest fun AP build I have tried out a couple times in norms
KZ Engel1 votesonly conq or lethal tempo
and guinsoo almost always comes first
sometimes even skip jungle item for ER and stormrazor
webstar19951 votes[{quoted}](name=KZ Engel,realm=NA,application-id=3ErqAdtq,discussion-id=XUhjUi11,comment-id=0000,timestamp=2018-06-20T18:13:52.299+0000)
only conq or lethal tempo
and guinsoo almost always comes first
sometimes even skip jungle item for ER and stormrazor
Acoording to OP.GG lethal tempo was never the best. Dark Harvest was the best wr rune for a while and PTA was the most used and 2nd best rune til Conq came out and took its place
Alex h87211 votesIn order of build> 
(sell ).
w/ E max is MORE than enough damage to melt tanks & squishies alike, for the tenacity, + double on hit trigger means you are dealing aoe damage if the enemy team is too clustered (plus ridiculously fast split pushing), and the extra beef from in combo w/ lifesteal makes you much harder to burst (unless you go in 1v5 on full hp enemy team like a potato), the carry potential of this build is higher than any other yi build I have seen or tried.
Runes: Precision always the same: Conqueror, Triumph, Alacrity (atk speed) and coup de gras, and for JG I always go celerity/waterwalking for extra power in the river skirmishes (plus celerity synergizes really well w/ yi ult), for lane yi in a tough matchup I'll sometimes go Boneplate crysalis, but in easy matchup celerity/waterwalking for extra MS and roaming power.
webstar19951 votesThe new rune in the sorcery rune page is better than water walking. The one that give you more move speed and you can move through units when you ult. Titanic hydra is not good on yi because you do not have much max hp for titanic to do damage. Ravenous is better and it gives more lifesteal for baron solos and extended fights. Not having qss or any armor is a recipe for disaster. Scimitar and ninja tabi replacing hydra and merc treds would be better
Alex h87211 voteslol no, these days HP + damage is better, yes QSS is very nice to have, but if you pick your engages smart, and clean up teamfights rather than being the initial engage (yi is best at being a janitor, getting those resets), you shouldnt be as worried about getting locked down.