Which Nakamichi to choose?

Having everything in alignment on a cassette deck can be compared to having everything set up correctly on a turntable, if something is off the sq will be off.

I think with the resurgence of vinyl and the old time vinyl addicts , setting up of a turntable is better understood and practiced than the same procedure for a tape deck.

Usually the correct set up of a tape deck is best left to those dying breed of specialists, mine was set up maybe 4 years ago and I have not had reason to question it having drifted or warranting another set up yet.

@orpheus10 
Right on, I truly never "compare" the cassette sq as such but it is obvious to my ears when it is especially good or bad compared to itself!

I have some superb tapes, and some really bad ones...lol.

I suppose one of my earlier comments stating it was as good as vinyl was not quite accurate as I truly do not compare the two, what I really meant was that when I played a really good tape, well it just sounded really good.

Once aligned and tuned my deck keeps it for quite some time. I also treat playback head with LAST tape head preservative before playing every cassette, it lasts for two sides. This is not a substitute for cleaning, of course, only a complement. When properly maintained Nakamichi head should be good for at least 10000 hours, I am not sure any head or just better heads.

This will provide a good test of the system sensitivity and your hearing. Get two Walker 1/2" resonance control discs, $50 each.
Place one very near Nottingham motor without it touching the motor holder, place another one on top of the deck where the transport is located. You should hear a slight improvement in clarity. If you don't - there will be a work to do. Nottingham Spacedeck is a very emotional, dynamic and quite quiet turntable, some people prefer it to much more expensive tables. Also, when recording from it, I can clearly hear differences in pressings when listening to the Nak. I can also compare cables and phono stage power cords this way.

@orpheus10 What are the odds I looked at the pic of your deck, nice looking deck btw, and there is one listed! Looks like a good buy for $550 if I was in the market I might snap it up.

https://www.audiogon.com/listings/lis93faf-sony-tc-ka3es-tape-decks