My gf and I used to have sex on the couch whenever her family would be out. It was a fairly deep couch, so she could lay with most of her back on it (head at back, cushioned part of couch, and pussy at front of couch). And I would kneel on the floor in front of her. It was a good position for fairly deep sex, as well as leaving hands free for much fondling

Not tried it yet, but I would love to do it on a train. Her wearing a skirt but no panties, sitting on me. Would probably only do it late at night though!