I actually find WMP11 to be pretty stable and work as expected on my XP box even if I have other things open.
iTunes is incredably flaky particularly if I have anything else open. I am getting used to it but I would not consider iTunes an ideal implementation.
As to which server I use to manage my music ... if iTunes would talk to any non-apple device, it would be a consideration. But it doesn't and WMP is the only one which does. What would have been ideal is for WMP11 be able to sync the music to the iPhone, avoid the iTunes copy entirely. But we know what Apple thinks about that don't we?
So I have my iTunes world now for my iPhone and my WMP world for everything else. Nere the 2 shall meet (unless I have to import new music or export depending on where its purchased or ripped).
I have never had iTunes be flaky on any of my Windows Machines and certainly not on my Mac Machines. But you are running an old computer as I recall. WMP is almost built into the Windows OS, so it should work well. However my complaint isn't in respect to that. It is more about the user interface, crappy ability to download album art and the incredible crappy manner in which is tags music.
Indeed it would be nice if WMP could be used to copy directly to the iPod Touch like you can with Copy Trans or the other half dozen programs that do so. So there are choices out there beyond and above iTunes. I would imagine it would be nice if iTunes could be used to copy music to the Zune too. None of these companies play nice and this just creates issues for end users.
Neither MS or Apple have very user friendly media programs if you ask me, but if I had to choose one and I guess basically I have, then it would be iTunes over WMP hands DOWN! Then again I've been using it for 4 years, you just started and we are all creatures of habit.