Which Nakamichi to choose?

I researched cassette decks from ebay 3 years ago and found "best value" deals on Nak CR3, one of which I bought and tested for a friend. It beat out the SQ compared to my refurb Teac V770 (which I also recommend) and to a JVC 3-head deck TD-V621 (which I bought for myself as a backup; not bad but not as good as Teac or Nak). I thought that most of the Nak 3-head decks circa late 80s-early 90s all looked good, but some were going for a premium price. The decks I considered were CR3,CR4,CR5,DR1,DR2,DR10, and Nak "Cassette Deck 1". A full refurb on any of them would be good to consider IMO. PS the CR3 finally broke down after 3 years according to my friend. No repair shop nearby where we live...

lowrider57

Proper bias is of course very important, but would you archive vinyl using Dolby?

I wouldn't choose to archive anything on cassette. It's just not an archival medium.

Had a Naki 600 back in the day. Only 2 heads but was impressive none the less. Got stupid and sold it. Had a 680 ZX for a short while which was also a quality device. Sold that as well. Regret that simmered over the years resulted in my finding another one - a 600 - and buying it from a fellow in Canada. 
Still sounds remarkably good with a quality tape such as TDK SA, Nakamichi,  Maxell EXII, or Fuji. Of course it couldn't tranform a sonically-poor LP into something good, and care had to be taken to not 'over saturate' the tape when dubbing.
Still sounds great in my 1988 BMW's stock cassette deck based audio system.

@cleeds

Not an archival medium? Depends. Cheap stuff, 120 minutes, agreed. Metal Type 4, 60 minutes duration, absolutely disagree.

I have tapes made 20 years ago that sound fine. I used the ceramic cartridge bodied cassettes for mixdowns from 15 ips master tapes. Just amateur stuff, but I made damn fine CD’s, if I do say so myself.

Without going into details, I think that cassettes are a perfect way to extend the life of precious vinyl. Tapes don’t degrade; vinyl does, at least on most real-world systems.

leoniruii

Had a 680 ZX for a short while which was also a quality device.

The 680 is an outstanding machine. I still have mine - it was expertly serviced last year by Soundsmith. I use it with a Nakamichi NR200 outboard Dolby B/C unit. When levels are properly aligned, the recording quality is amazing. I keep it on hand to play a few historic recordings that I have and the occasional old mixtape. But, as a practical matter, even the best cassette deck is obsolete. And a good reel-to-reel deck will walk all over it.