So no one actually use OpenSUSE here? Bummer.
Whether or not someone uses opensuse is most likely irrelevant to what you're looking for. If you're comparing <insert linux distro here> to vista, most people who are going to give you reasons why <insert linux distro here> is better has nothing to do with an individual distro, but with fundamental linux strengths and weaknesses.
I myself use linux exclusively. At work and at home I use Gentoo, and on my laptop I have Xubuntu. Ubuntu and Gentoo are completely different distributions intended for different users, and have different strengths and weaknesses in how they do things. However, the reason I use them over XP remains consistent cross distribution.
My reasoning for using Linux over Windows (XP or Vista) is numerous. First, it's free (as in beer). I don't have to worry about licensing, either on the OS or the other distributions. When a new version comes out, I can upgrade without worry. I can install an office suite for free. I can setup antivirus software (if I wanted to, which I don't) for free. The database servers (both postgres and mysql) I use on my servers are free. As is ldap. As is samba. As is Apache.
Second, it's free as in freedom. Meaning that what is installed on my system (sans the nvidia drivers) are all open source. Why is this important? I'm not much of a C coder, so I'm not going to personally fix something myself if it's broken. But if <insert window manager here> has a great innovation, other developers can browse the source and learn from it. More importantly, if one application gets stagnant, that can be forked into side projects. A recent example of this is Compz -> Beryl -> Compiz Fusion. The open source development model breeds innovation. Vendor lockin stiffens development.
Finally, it's about choice. At one point I got tired of gnome and the way it handled things. I tried Xfce 4.4 (now I'm on the xfce 4.5 svn). It's wonderful. I've tried kde, gnome, xfce, windowmaker, enlightenment and openbox. And that's just from a window manager / Desktop environment standpoint. Linux is about choice and customization. It's about easy application installation through package manager.
The greatest showing of choice is through distributions, which is why the strengths/weaknesses of opensuse is almost irrelevant in a discussion about Vista. Linux offers you choice. Every distribution is fundamentally different. A system like Gentoo has different strengths/weaknesses from a system like Ubuntu. With Gentoo, I can customize every single component on my system, installing only software I know I need, compiling in only options and dependencies I know I want, running my own customized kernel, and build my system from the ground up. There isn't so much of a Gentoo 'release', as a release is just a snapshot of what's in the portage tree, and you can upgrade to the latest 'release' at any time with an emerge. The downside is it can be a long install process, and compiling software is lengthy. Ubuntu, on the other hand, is an easy to install, easy to use, up to date distribution that tries to make itself as accessible to the end user as possible.
In short, it's the choice that makes Linux markedly better (in my opinion) than Windows. If I was writing a report, that's what I'd use as my basis. Choice and freedom.