- APT and dpkg, these tools make life so easier that is difficult moving to anything else.
- Debian web tools are great to keep track of any package and discuss anything with the Debian community.
I do not use:
- SUSE Linux because YaST has always got me headaches (different problems with different versions of SUSE) and I do not like the Microsoft-Novell pact.
- Gentoo Linux because it is not a practical distribution as you have to spend ages recompiling software (you can also do that with Debian if you want) and is definitely not user friendly as you have to configure too many things where a distribution like Ubuntu (or even Debian) provides sane defaults. Take a look at this video of Gentoo Linux installation.
- Fedora. I would try it if it did not use RPM that I dislike. Fedora also has some problems that you will see quite early like font rendering. Fedora is also a good candidate to a desktop Linux distribution but I have found that Ubuntu is just more polished.
- Slackware. Just do not use it. Having simple packages with no dependencies can give you major headaches.