1993. I was thinking about replacing my aging A500-system back then and had a good amount of money to spend. The choice was between a new Amiga (1200 or 4000) or a new pc. The amount of 486s to be found was overwhelming, the amount of Amiga shops was, well, not.
I bought a 486dx2/66 with 8 MB ram, 245 MB harddrive, 2 MB VLB card, Soundblaster 16asp with a 17" CRT and an internal 14k4 modem.
It was running Windows 3.1 and was damn powerfull with great software. True, Windows 3.1 wasn't as good as Amiga OS 3.0, but the software it was running (Lotus Amipro, some graphics software, other stuff I can't remember) was absolutely great.
The pc definitely won. It was easy to expand and tinker around with, you could use several different operating systems if you wanted to, hardware was easy to get and cheap, as was software.
Amiga hardware was expensive and hard to get, as was software for it. Productivity software on the Amiga was lousy compared to software for the pc. There was nothing back then on the Amiga which compared well to, for example, Lotus Amipro 3. Support for the Amiga in computermagazines was in heavy decline.
Since then, I have used a pc for my normal computing needs and other computers such as the Amiga just for fun, whether it be nostalgia, gameplaying, fooling around with a different OS or whatever.
So, all in all, for me, the Amiga lost in 1993. I have been very satisfied with the 486 I bought back then, which I have been using and upgrading as my maincomputer until 1998. The Soundblaster 16ASP was a very good soundcard for its time and the Diamond Viper (2 MB VLB videocard) combined with an Iiyama 17" CRT gave me fast, crisp and stable videoperformance.