I'm a left handed person and I use the keyboard with my left and mouse with my right, just like a "right handed" person would. I don't like you generalize all left handed people as "keyboard right, mouse left".
Anyway, on the topic of WASD vs ESDF, for me the E on ESDF is too far offset to feel comfortable. Also if you lose WASD easily I feel you will lose ESDF even faster, at least WASD has some big keys next to it to help you feel your way back on them.
Also I use shift and ctrl with my pinky, and reaching shift and ctrl from ESDF is a bit further out than comfortable for me. Not that I can't do it, but I'm pretty sure having my pinky out at that angle is going to hurt in the long run.
So yeah, WASD for me.