I had a very nice stay at Christian's place, "right in the middle of things" indeed, close to S+Ubahn, markets and shops, and to night life too.
Check-in and communication were quick and easy. The room was cozy and very quiet, I particularly loved the big window next to the bed facing the main street.
You really get to live like a local in the fascinating Friedrichshain neighborhood. If this is what you're looking for, it is going to be the best place.