I am used to z/x because I tend to use the side of the laptop to cancel out my rebound. But my major finger for osu is actually my middle finger instead of the usual so I hit z more often than x
X/C because I used to accidentally hit the windows button all the time.Each time I buy new keyboard I do this http://s019.radikal.ru/i644/1404/f4/d123be1ddafe.jpg
Why dont you use z/x and how does it work well with the way you like to play.I tap faster with Tab + Q.
I started playing with a/s and i do this because I arc my fingers over my keyboard the the added height improves my clicking speed by monstrous amounts making it easier for me to slow down to the right speed and get perfect accuracy.