In the other hand we can't compare Linux and Windows (XP or whatever).
The thing is that Linux is the core; the kernel. It's fast, safe, and horribly stable. (Have you ever let your Windows box open for 3 months without rebooting? :P)
Now the distribution (you're talking of Ubuntu) takes that core and adds applications and customizes stuff upon it. And then comes into play the Window Managers, like the very popular Gnome and KDE. These are the Graphical User Interfaces of the Linux DISTRIBUTION. You can choose which one to use (for example, Ubuntu comes with Gnome and Kubuntu comes with KDE).
These GUIs have very different behaviors and very different resource needs.
If you run Gnome with Compiz (the thing that makes your windows like jello and the cube and all these effects) having all options turned on, you'll very likely find that it is not much faster than WinXP if not slower. But if you run XFCE (another GUI) you'll very probably end up finding that you're computer is much faster on Linux (USING XFCE).
So is there one better than the other? I'd say yes: Linux.
Is there one better than the other for a gamer? Yes: Windows.
Is there one better than the other for a programmer? Depends; is he developing exclusively for Windows? If so: Windows, else: Linux.
Is there one better than the other for an electrical engineer? Yes: Linux.
Is there one better than the other for an everyday person who reads his mail and doesn't care about anything? Yes: Linux; it's free.. Money but aside? No: they'll do the same job, but still, on Linux you're infinitely less likely to catch viruses for example.
May I suggest you to try Linux Mint. You talk about Ubuntu, but Mint is based on Ubuntu, so it's just even more plug'n'play and you should really not be deceived! :)
I installed Ubuntu on a spare machine I have at home and it works great no compliants. I need to install a few drivers and I have to admit I have been slacking in accomplishing this. Are there any specific questions you have that you want to compare between the two operating systems that would help you in your decision?
I went through the whole suite : 7, Vista, XP, Leopard, Tiger and Ubuntu. My decision ended up being Ubuntu. It does everything Windows does so much more stable and smoother. It is my main and only OS. I have not hit one issue. And the interface (whichever you choose) is great. NTFS-3g is an awesome piece of software, helped me out a lot, Samba was easy to install, Second Life works, the documents made with OpenOffice.org are nice (without the ribbon interface), everything works for me. And for the fact that for the average user it is better (the risk of viruses is very, very, very small, and sudo and other require a password, so he can't mess something up that easy). And not only that it is better, it is a hell of a lot cheaper and more customizable. And if you still want to say : 'I want MS Office' I'm telling you're insane and you can use Wine, VirtualBox, VMWare, ... (all free).