Ubuntu upgrade: smooooth
I'm beginning to think that smooth continuous upgrades are the single most important feature in an operating system. It really doesn't matter if the first installation doesn't succeed. I can always do the installation again. But when I've accumulated (over the years) a set of desirable software, numerous configurations and local tweaks, I really don't want to start all over again.
After some months, and perhaps years, those tweaks and configurations become so invisible to myself that it seems that I could start with a fresh installation. But however smooth and nice an installation is, I always end up with a system that just isn't quite what I'm used to. Thus it always ends up in painful tweaking session that takes several hours, at least.
That's why I really love systems that allow me to do major upgrades without much trouble. That's what Ubuntu gave me. Gotta love Ubuntu.