As always on used machines it comes down to fitted head stack and remaining head life.
I have a habit of purchasing Otari Machines when the need presents itself, as the US office is close to my operation. The machines have good parts support and are fairly easy to "hot rod".
As for the Otari MTR 10 machines I try not to pay more than $500.00 USD(not including shipping) for a two track machine. I usually modify the machines into format specific uses.
Parts show up fairly regularly on Ebay to expand the function or maintain
the machines (i.e. Time code heads, revolvers, Control cards, Audio I/O'S
etc.)
The other machines mentioned in your post are solid machines, but may cost slightly more money to refurbish and maintain.
Just my 2 cents.
Cheers!
Bruce Maddocks Cups 'n Strings Studios