KB/M is objectively better for some games such as FPS, and you'll often be chewed out by PC elitists if you mention wanting to use controllers. Still, there's a lot of console ports on PC these days that arguably work better with controllers, and I like playing on my TV, so I use them quite a bit myself.
Currently playing: Crusader Kings 2 (PC), Super Mario 3D World (Wii U)
How do you even play fighting games or AC series on kb&m??
I could ask the same with regards to how consolites play their CoD/Battlefield/ etc using a controller.
To answer your question, with regards to fighting games, I would personally map the movements to something like WASD, UJHK or even the Arrow Keys themselves. Usually, the movements key will be control by my right hand.
To launch a special that involves, say QCF, I will slide though both the Down and Forward key in one motion. HCF? I will slide from in one motion from the Back, Down and Forward. Naturally both QCB and HCB are in reverse. Dragon Punch movement? Forward, Up, Forward + Up in the order.
The only types of movements I've never been able to pull of are those that involves 360 degrees movement(eg. Zangief's Spinning Pile Driver, Iron Tager's Genesic Emerald Tager Buster), hence I cant play grapplers. Also, werid inputs like Geese's Raging Storm or Hazama's Astral Heat.
Action speaks louder than words. But words, when used right, overwhelm any action - Me, 2006 Let's put a smile on that face - The Joker, 2008