My small classic puzzles and one medium classic puzzle due to their - a) ease of use (I find them very quick to get in and out), b) brilliant back pocket for items I want to get to quickly (eg house keys), c) great security - living in central London I have no concerns at all carrying one of my puzzles anywhere even on public transport, and of course, d) their slouches which still and always will make me smile and admire their beauty.