I am going to cheat and answer this a little differently. I am going to answer the question of "what was the most important audio purchase I ever made"?.
The answer was a pair of Thiel 2.0 speakers in 1985. Not that they were all that great but the options back then were pretty limited. What they did do was start me on the road to being a dedicated "follower of fashion", whoops I mean a dedicated follower of the Thiel brand. I am now on my fifth and last generation of Thiel speakers, the 3.7's, which are phenomenal speakers. It is was great loss for the audio community the day Jim Thiel died.