Big cubes, really big cubes. Instead of turning and processing information at max speed I enjoy the slow almost meditative aspect of constructing bars on big cubes. Best enjoyed with some good tunes in the background.
I think doing slow solves and trying to be very efficient is the most relaxing for me. If i time myself its still enjoyable but definitely not relaxing anymore. I think maybe once i start doing 5x5 and up or learn to solve the last layer of my megaminx those puzzles can be nice to solve on the couch.