Every side, I flip flop probably a million times throughout the night... I think for the most part probably my right side though, that's usually the position I fall asleep in the most, but then throughout the night I flip flop forever. XD
I usually sleep on my left side, but since my knee surgery I've been having to sleep on my back. My knee tends to hurt a lot if I lay in any other positions.
Unfortunately since I've become more mobile in the last couple weeks, I've been rolling around a lot more in my sleep, and for the last couple nights I've been woken up multiple times because I inadvertently rolled to my left side and woke up with really bad knee pain. It sucks
I sleep on my left. When I dislocated, and later had surgery, on my left shoulder, I had to sleep sitting up a bit. It was awful! My cats, the little dears, did their part to help - Maggie slept in my lap and Raven was between my feet. Two years later, I'm still trying to convince them that I really can sleep on my side now.