Cassette decks are a double edged sword. The best ones were (are) capable of astonishing performance, with a few of them in the list below even surpassing some R2R’s.
However these great “holy grail” machines cost a lot to purchase nowadays and will require a complete service (mechanical overhaul, and calibration) and in some cases at least a partial restoration in order to recover their legendary performance.
Here are some of these monumental machines to look at (in no particular order):
Nakamichi 1000ZXL, 700ZXE, ZX-9, ZX-7, Dragon, 682ZX.
Tandberg TCD-3014(A), TCD-911
Aiwa XK-009, AD-F990, XK-S9000
Revox B215S
Pioneer CT-A9X
Sony TC-K777 (ES)
The above machines are, in fully operational and calibrated states, capable of making subjectively indistinguishable copies from masters, making them all fantastic recorders. The Nakamichi Dragon has the singular distinction of employing an elaborate automatic azimuth on the playback head, making it, combined with its overall excellent quality, the ultimate playback deck, though it is also a state of the art recorder. However the ultimate recorder is the 1000ZXL, followed by the other above Naks and then the above Aiwa decks, in my experienced opinion.