User blog comment:Daywombat/AP Yi mid/@comment-9713132-20130420021445

AP Yi is one of those picks that excel against un-coordinated teams or with a co-ordinated team - he has a natural AD steroid that still makes his AAs hurt, and he can basically chain Alpha Strikes if he manages to get a kill / several assists.

AD Yi is technically 'stronger' because his Q is more of a gapcloser utility skill then your base damage which gives him leverage over traditional AD carries, he has a built in AD steroid which when, fully active (the passive bonus plus the active bonus from Highlander's reset) provides more AD then a fully stacked Bloodthirster. That, combined with his passive AA reset and a MS + AS steroid makes Master Yi a very, very, very strong fighter.

People use AP Yi because he's actually quite reliable in lane, being able to safely harass and wave clear. His heal is also a very broken ability - with enough AP, I've managed to tank the damage mid-game from an entire team through my channel. The reset on his Q due to Highlander is by far the most damaging combo in the game, provided it's done correctly.

I don't know if I answered your question (or if there even was a question) but that's my two cents.