In my case it would be a tie between a Yamaha CT 1010 I bought second hand for about $30 in the mid eighties, and a Sumo Athena, which I picked up around 1992 for $100. Neither are the best of course, but I still use them every day, and have built the rest of the many system iterations over the years around the phonostage built into the Sumo.
She's put up with all other replacements over the years, until seeming to say "all right, that's enough. It's my turn again".