I prefer AD. I think there are more correct build paths to choose from when building AD compared to AP, where items builds seem limited. That is just my preference though. Who do you think are the current strongest champions? In terms of AD or AP and build paths. 
The major difference is: AP damage is primarily dealt in quick bursts and comes from skills with CDs AP types are much more heavily affected by enemies building health AD damage types generally do not have nearly as much burst, and in turn they get sustained damage with auto attacks AD types are much easier to itemize against since armor is cheaper and there are more AS slows and such than skill blocks
there are no ad/armor items.
^except for lategame adcs who both burst squishies and do reliable dps to tanks
even though i play ad champs nearly every ap champ gets close to 700 Ap if they're the AP carry. ad carry gets like 300 tops
Strongest in each role? Probably, currently, for AD due to his ridiculous W passive and ultimate, and 
for AP due to his insane range and still insane damage.
AD is stronger. They get both sustained damage and strong burst(IF they have AD scalings such as 
). However, I like AP more because no one will ever beat 
me xD.
