I shoot 35mm mostly, but I have used 120 in my studio classes at school. I prefered being about 5 or 7 feet away. I'm a quiet, reserved person, and the distance kept me relaxed.
I bought a 70-200mm lens for my 35mm camera because I've been getting in to concert photography here lately, but I have used it for portraits a few times. Using a lens that long, I did have to back up a little bit more (I have to be about 4 feet away for it to even focus), which I like.