Since I work in a very busy suburban public library, I see a lot of interesting books come through. I have been casually reading about Linux and Apache and MySQL and other similar projects for the past couple of years. I came across a book done by PC Magazine about Linux, and it included a CD with Knoppix on it. I decided to try it out on my Dell desktop (our family PC running Win XP). For some reason there was a problem with the display, and it looked too strange to use.
When I got my parents' old PC, I tried the Knoppix CD and the display looked fine. When I tried to open programs like Open Office, or Internet browsers, there wasn't really enough memory to run them (since the live CD boots using RAM and not hard drive space, this shrinks the amount of memory considerably). I was impressed by the clean interface of KDE and thought how great open source software is.
After reading through my book, I decided to choose Debian for its stability and its many different software packages. The book described Debian's relative stodginess, that years can pass between new distributions, while other Linux distributions are out on the cutting edge. Well, my interests are in stability, not cutting edge, and I have been approaching this cautiously, so the seeming conservatism of Debian is actually attractive to me.
So Debian it is!