I don't see a reason why anyone would pick ap or ad. If you have ad master yi go up against ap he will completely destroy, expectially with the nerf on ap yi.

Why would anyone go ap yi? Ad was always stronger (people just thought ap was strong because of the heal...) I had an ad yi basically take out 5 people on the enemy team solo. They came in 1 by 1 and died one by one. And he was basically able to finish the game off single handedly.

AP Yi isn't played because of the heal.

Just throwing that out there.

The thing about AP Yi is if you play him right he's really easy to pull off a pentakill with. His ultimate when turned on means that any kills he gets resets all of his abilities. With a high damage technically aoe nuke that means that he can cast that up to five times if he uses it right on an enemy team, and if he times his participation in a team fight just right he can clean up a fight even if the rest of his team was losing to begin with.
Unfortunately this places him in an awkward niche role with a very high skill necessity which means that he's hard to pull off correctly, popular because of pro-player picks, and limited use on the battle field. But if you do it right he can be a monster in his particular role.
Unfortunately as well, most teams need a high damage and utility role in the mid lane, something other than a strict sustain killer, which again puts him in a niche role.

tl;dr. He's a strong niche pick, but he has to fit a very strict role on the team and can't expect to do more. AD Yi has more use arguably but doesn't have the easy-pentakill kit use like AP Yi.

Ok so you get the Q that does some what insane amount of damage. Then what? Ad yi can use his q too, but then after all the %crit and lifesteal built up he will just demolish an ap yi.

Can you tell me a reason to why ap yi would be better than ad?

I see your point. But you are mainly focusing on getting penta's. An ad yi with infinity edge, and phantom dancer can blow anybody else out of the park. As well has clean up. He can litteraly 3 hit the carrie's, and use his ult to catch up to anybody else. Especially with his passive he is just a monster. AP yi is good for his q and heal, but ad yi is good for everything else lol.

You don't say Champion A is better than Champion B because Champ A wins in a 1v1. The problem with AD Yi in draft pick is that he's so easy to shut down, as hard CC = instant death for AD Yi.

All his damage is front loaded into a nuke, rather than having to chase down people and hit them. While AD Yi could potentially do more damage, kiting him with any other CC other than slows is incredibly easy. AP Yi, you can't CC him while he does his damage. If he kills even one squishy person, he will Alpha Strike again for large amounts of damage. This is opposed to Yi having to run up/alpha strike up, attack for 5-8 seconds to kill someone.

AP Yi is on demand damage, hard to CC. AD Yi is damage over time, easier to CC.

Does that not go for AP yi aswell? When Ap yi starts his heal and you cc him to cancel it does that not make it an instant death for ap yi too? Even if he doesn't start his heal ifyou stun him that's basically an instant death too.

"As hard cc = instant death"

That go's for basically ANY champion that doesn't stack hp and armour/resistance. you get hard cc on an ad carry? Dead. Hard cc on ap carry? Dead. That can go for anyone.

It doesn't take that long to kill someone on ad yi. Especially 1v1 o.o

You act like 1 Q on ap yi will instakill. Maybe that's the case for a FED ap yi. But the same can be said for a FED ad yi. A fed ad yi will do more damage than a fed ap yi.

Scenario 1 :

AP yi does his Q. Does significant damage but AA's don't do much and takes a while to kill enemy.

Scenario 2 :

AD yi does his Q, catching up to his enemy doing minor damage, but 2 hit's because of %crit and overall attack damage.

See where I'm getting at?

Also, I accidentally up voted your post when I wanted to quote it lol.

Along with all the issues of AD Yi, melee carries are really underpowered at the moment, so if you build straight damage you can't expect to do a whole lot. Being an assasin is way better and AD yi is better as a pubstomper when no one knows how to handle yi, while AP Yi you can't really do anything against if he's casted his ultimate and alpha strike (except run away wasting time on his ult)

As Im S0fa King said, you can't compare two champ styles with each other in a 1v1 situation. AD Yi and AP Yi are played differently, and both have their ups and downs.

AD Yi relies on lifesteal. Essentially, he uses his skills as utility to reach his targets and keep them close. Then he uses his lifesteal and high damage output to outsustain and outdamage the enemy.
If he gets stunned, he is unable to hit, thus being unable to heal HP, and can be burst down in seconds, even if he tries to Medi-tank.

AP Yi relies on actually killing his target. After he gets Lich Bane, he has a two-part burst: his Alpha Strike, and his Lich Bane proc. Because both have a fairly short cooldown, he can burst entire teams down in a matter of seconds, well under the time limit of his ult. On kill, his timers reset completely, and he can ult again, and start everything all over again. A much higher risk/reward scenario, but potentially even more dangerous than AD Yi, because his entire combo gets reset instantly on kill, which could mean disaster for the enemy team. If he gets stunned, he could potentially get bursted down quite easily. However, if he has yet to use his meditate, his Medi-tank is significantly stronger than AD Yi's. He could sit right in the middle of the fight and not die unless your team uses up another hard CC on Yi (which could be largely detrimental to their teamfight ability). Not to mention that his Meditate lasts 5 seconds, which is just about enough time for him to wait until his Alpha Strike is ready again, unlike AD Yi, where any second spent meditating is another second spent not dealing damage.

Both can be used; AD Yi and AP Yi are both quite scary when your team can't fend them off properly. However, AP Yi can dish out potentially much more damage than AD Yi and also has a better chance of surviving.