If you're migrating from Ubuntu and used to using the DPKG package management system (apt-get etc.) then I suggest giving Debian testing a look. Debian by default doesn't insist you use any specific desktop environment - you can choose which you prefer. I like XFCE for its minimalism, speed and similarity to Gnome 2.
Debian Stable is good if you want something rock-solid stable, with timely security updates released from the security team, but if you like to play with software newer than 2 years old, you might be disappointed by the age of the software in the repository. Debian Unstable contains the latest packages from the original software developers that have been rolled into the Debian package format, but may contain system breaking bugs. These packages are typically moved into Debian Testing after a few weeks of basic testing, so it's a comfortable place to run if you're a power user and want to run fairly up-to-date software.
The different software projects are always going to be updating, adding new features, following their roadmaps, so to a certain extent change is inevitable, although this is by no means a bad thing. A lot of the under-the-hood changes have made system administration much more consistent and simplified.