A Nakamichi in good working order is the best cassette deck you can find. I own a Dragon and its playback is flawless. Tandberg and Tascam also make nice decks. There are differences in playback between machines of the same manufacturer. I would look for a 3 head deck over a 2 head. In a 3 head configuration both the playback and record heads are separately optimized with respect to their alignment.
