I have made some good purchases from pissed-off-wife's. Also some widows. You would be surprised how often they want to get the 'stuff' out of the house, being the gear was always the guy's first love.
The question is too general and too ambiguous to be answerable. But depending on how "most sought" is defined, a good case could be made for Western Electric speaker drivers, tubes, and tube amplifiers from the 1930's. As to why, because they are extremely rare and, if in good condition, they are apparently extremely good.
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