I started to use Linux in 1994 with a Debian distribution. It worked quite well on a 133Mhz Pentium with only 128Mb of memory. It was stable and gave good performance (given the memory and speed of cpu at that time).
Then, I have used a Linux Red Hat distribution, starting at version 5 and then 6. It was in 1998 on a 300Mhz Pentium II with 256Mb of memory. KDE and Gnome were not there at that time (if my memory is right) and the X11 environment was not as powerful as today but worked reasonably well.
In 2002, I decided to switch to a Mandrake distribution because it was close to RedHat and it offered a better support for French language, more applications. The switch was easy: the packages are managed in the same way, some administration tools are specific to Mandrake but with a simpler and easier interface. Mandrake did a good job at simplifying the interface to end-users. I started with a Mandrake 8.1, upgraded to a 9.1 and then 10.2. However, each time I did an upgrade, I made a complete installation (because I added a disk or switched some hardware). One of my system was not upgraded and it stayed in Mandrake 8 because the system was remote (it did not have a display) and the remote upgrade was difficult (at least, I didn't know how to do it). Each time I upgraded, the KDE environment had different behaviors. Not big differences, but still annoying for a end-user (different behaviors on the mouse, the keyboard and how you type accented letters, keyboard shortcuts that changed, menus that changed, the session restore that worked differently or did not worked, ...).
In 2005, I have been convinced by my colleges at Solsoft to use a Debian distribution. The administration and installation of packages was supposed to be easier, and the system upgrade was possible remotely. Well, I had to learn the Debian packaging stuff (I was used to the RPM) and I was using Debian at work since 2002, so let's try it. The installation was easy and worked well. Again, the KDE environment, the keyboard layouts, system behavior became different compared to Mandrake 10.2, but after some adaptations it worked (still it takes you some time). Then, came the problems. I needed specific Debian packages and they were in the 'testing' category. I installed them and of course broke some package dependencies. That's a nightmare and always a hassle,... but with some time and Debian administration knowledge I've managed to solve the problems.
Meanwhile, the Ubuntu distribution came in. The big difference with Debian is that the distribution contains packages which are updated more regularly, work well together and appears to be much more tested and stable over time. The first computer I've switch was my Linux router and I have installed the Ubuntu Server distribution (the server was running a heavily stripped-down Mandrake 10 distribution). The Ubuntu Server distribution was installed easily and it contained quite all the packages I needed. I also installed a few specific packages for monitoring, backup system and everything went well. Upgrading the packages is similar to Debian (since it's the same package tools) but it appears to me it's a little bit more stable.
Then, I decided to switch my desktop station to use the Ubuntu Desktop distribution. It's probably the easiest installation I have ever seen. It worked quite out of the box without having to specify or tell any funcky parameters. But it was too simple: not enough utility packages, no development package, no KDE, the printer setting was a nightmare (USB printer). Anyway, the system works now but it required quite a lot of Debian/Linux administration knowledge to set it up. Basically, the problem lies on the Gnome, KDE, X11 and user applications that come with the Ubuntu Desktop.
Despite the Ubuntu Desktop installation issues, I'm very happy to have switch to Ubuntu. I guess this is the Linux distribution that will give me less problems in the future, will allow me to stay reasonably up to date with new packages and security fixes. The Ubuntu community has still some progress to make to package the distribution in a way that non-Linux users can use it. That's their challenge.