You don't say what your budget is or what you want to do with the machine...
Personally if I was looking I'd not want anything older than a 'D' series Deere or a 'D' series Case... and really not much older than a 'K' series Case.
I also find it hard to stomach anything older than a 'D' series Ford, preferably a 555 or larger. 416 Cats are good too... although always beware of the brakes on the Cats. They use Ford drive components which are fine IF they use the correct oil. Most Cats seem to run the wrong oil and owners don't add the friction modifier that they should... so you see a lot of them with the brakes shot at 5000 hours. That's a big internal mess to clean up not to mention a big expense.
JCB also makes a very good hoe. That's also an area I'd stay with at least a 214 model instead of their older ones.. particularly an old one with a Leyland engine.
MFWD is a definite asset on backhoe... so I'd certainly be looking for one with mfwd; probably in the 15K+ price range.