Difficult question.
I bought myself a Nascom 1 kit when they were introduced, but I never got around to build it. "building" was really just putting chips into sockets, but you also had to provide your own power supply and that turned out to be a difficult snag. +12, -12v, +5v at least, and maybe also -5v - not sure about the last one. And also had to be able to put out a couple of amps IIRC. Couldn't build one, couldn't buy one, summer came, school started again and we had AIM-65 computers to work with at school. But I also used the school's minicomputer (with core memory). And then 2KB of RAM was kind of obsolete so the Nascom stayed in its box, unassembled. So, it was the first computer I bought and owned, but I never actually used it. At least I still own it.
Then over the years I worked with lots of different computers, mini and micro. Apple II, Norsk Data mini, CP/M boxes.. 6809, VAX/VMS. At one point I bought a British-made almost-clone of an IBM PC (I remember I had to call the import company about why I couldn't get it to work with a harddisk - turned out that some interrupt vectors were different in the BIOS. The guy on the phone told me what those differences were, so I just burned a changed version into a new EPROM and it worked).
The next computer I bought was after the AT was introduced, it was a Taiwan-made AT clone with 1MB of RAM and 40MB harddisk. Good computer, and I wish I still had it.. now. I paid an absolute fortune for it. After just a few months the disk was full and I had run into the limit for what it could do. Gave it away to someone in Russia at one point (after it became legal to do so, of course. Wow, all those regulations.. Norsk Data made a 32-bit mini which was modified for export purposes.. some of the address lines were cut so that it couldn't address as much memory).
Edit: Well, I also bought a programmable TI calculator in 1975.. don't know if that counts!
-Tor