George Moffat, world Open Class Champion in 1970 and 1974, wrote that if was first into a thermal, he would always circle to the right, because most pilots circled to the left out of habit and therefore were less efficient when forced to thermal to the right.
Indeed, I always tend to throw it to the left if the thermal is indistinct. As Miserlou says if you're right handed it's more natural to wang the stick to the left than the right. I know I do this so make myself turn to the right every other thermal, unless it's obvious which way to turn ie the wing tip moving.