Project skins (Master Yi, Fiora, Lucian, Leona, Zed, Yasuo)
Battlecast skins(Vel'Koz,Cho'Gath,Skarner,Kog'Maw, Urgot, Xerath, Viktor)
Mecha Skins(Malphite, Kha'Zix, Aatrox, Sion)
or maybe the new Program skins (Lissandra, Soraka)
I think Battlecast Skins are the strongest and the Program Skins are the second strongest. Lisa and Raka could probably just hack into the Project and Mecha Skins and render them useless.
The strongest mechanical skin is the SUPER GALAXY 
https://youtu.be/fF0EM1_6BgM?t=18
http://pre01.deviantart.net/e859/th/pre/f/2015/068/1/d/super_galaxy_rumble_by_muffonio-d8l4j3n.png
Because has the drill that will pierce the heavens.
I believe it was said that Batttlecast Cho has a sonic attack that is measured in exawatts. IRL, the world's power output, that is EVERY SINGLE POWER PLANT IN THE WORLD WORKING TOGETHER, has an output of about 18 terawatts.
This means that BCP Cho'Gath has an attack that is more powerful than a laser powered by every power plant in the world, by a factor of at least fifty.
So I'd say him. Or maybe SG rumble.
Project skins, dat Fiora hip
"Submit to my designs." ~
