Standard: QW
Taiko: QW ]\
CTB: QW space
Mania: All default, though I'd like to eventually find a comfortable configuration for 5K and 7K.
I have a gamepad on my keyboard which is what the Q and W keys I use are on, and I just got so used to how they feel in standard I ended up using them in other gamemodes as well. Patiently waiting for a 2 switch keyboard with reds to come out from osu!, but I imagine the transition will be uncomfortable at first.