I guess I'm a rather unusual case, but I consider myself right handed for the most part, but I ALWAYS masturbate with my left hand.
Although, my right hand is the one I use to write and draw with, my left has always been used to wipe my bottom, open jars, and the occasional maneuvering, anything, I suppose, that requires less conscious activity, but requires more bodily processes. At least, I'm just guessing.
Whether it's just holding onto a vibe or thrusting, it has to be used with my left hand or it just doesn't feel... quite right! When I use my right hand it can be compared to an "awkward" lover: it just doesn't know quite the right intensities and tries to approach it logically, but it just doesn't provide that intuitive "oomph" my left hand does, which I guess is more of the "passionate" lover type, ha ha.
I asked my dad awhile ago which hand he used to masturbate with, and he said left too when he is a righty, so, you never know! It's funny how we share this trait, ha ha.
He also does similar things with his left hand too.