WASD, non-inverted Mouse, and occasional use of controllers (I have 3 total).
I use a 6 buttons layout MadCatz controller (6 buttons Genesis style) for Fighting games, and a third party Wii U Pro controller (identical replica of an original one) for occasional games where it's preferable to use a controller, like some older 3rd person console ports, or the very rare racing games I do play. But outside of those exceptions it's typical Mouse + WASD.
I have used the directional arrows before for some online FPS games, it worked out well enough for movement. Instead of WASD that is. So I had some keys on my left like R-Crtl, R-Shit, Enter, Backspace, some at the top like the usual Insert/Home/PageUp/Delete/End/PageDown, and some to the right on the number pad portion. I used that setup for online games (mostly, although not exclusively) with a lot of prefixed voice-based and/or text-based commands for communication with my teammates. I would customize the controls to assign many of those keys I had left, up and right to specific commands or voice lines. I used the directional arrows setup all the way back when I played the first Natural Selection, for example.
And my use of the directional keys stems from my first foray into PC FPS gaming, from much older days when I played the likes of the original Quake, Duke Nukem 3D (I think, not sure about that one) and Unreal. Maybe Doom as well, although not sure which one (most likely not Shareware / Ultimate Doom, I'm 99% sure it was Mouse-only back then). When it comes to PC gaming the directional keys (with the Mouse of course) is a setup I kept all the way from the first pre-built PC I got to the release of the Orange Box and TF2 (with my first custom-built PC), which from what I can remember is about when I started to use WASD. I still remember today how back when I was mostly a console gamer and had just bought my first gaming-capable PC, how the concept of using 'keys to type sentences' would be used to move characters in a video game was incompatible with my brain. I just couldn't fathom how people could play a game with a keyboard, much less somehow using any of the lettered keys which - to me - existed for the sole purpose of typing text.
So yeah, eventually I got curious enough I guess. I can't recall exactly what was the process or the trigger that initiated the change of mind but I do recall getting a new keyboard around the time I had bought the Orange Box (and I remember it was a Logitech one) and talking about how 'weird' it was to figure out how to play this game on the Keyboard outside of the directional arrows (referring to TF2) on the mic to others in the team. I think that perhaps one reason for me (for going WASD) was the physical layout of keys and maybe the width of the keyboard. It might have been something as simple as me realizing 'Hey wait a second... this is comfortable, and it works!'. I never looked back since, always stayed WASD.