1. File system, Windows uses the NT File System which is the main reason why you have to defrag. Ubuntu uses I believe ext4 which does not fragment and therefore does not need to defrag and never slows. Even though this file system seems perfect there are other new ones being worked on that are even better and in the next few years will be implemented like btrfs.
I believe the above point doesn't matter if you're using an SSD where fragmentation is not an issue? Correct me if I'm wrong.
I agree with everything that DMGrier has said. Although, the OP appears to be new to this sort of stuff, and you used jargon and terminology which might be a bit overwhelming for someone new to Linux.
Anyway, I've been a Linux user for two years now (Currently running Xubuntu, which is a lighter version of Ubuntu with a pretty desktop manager), and I do most of my daily computing on Linux now. DMGrier mentioned most of what had to be said but I can add to it.
First off, I think which is the most beautiful feature of Linux, is that you can choose your own "flavour" of it, known as a distribution (or 'distro'). Ubuntu is the most popular one, but there are dozens out there. For example, my netbook which only has an Atom processor and 2GB's of RAM runs horribly slow on Windows. It takes several minutes just to get to the Welcome screen. But after I installed Xubuntu on it, it totally breathed new life into it. It's a low-resource distro which doesn't tax your system. You can pick and choose whichever has features you like (for example, Kubuntu has a gorgeous user interface and high-quality desktop features).
Next, you don't need to manually install hardware drivers. Linux does that automatically for you! I was blown away too when my WiFi adapter worked straight away when I used Linux for the first time.
Next, if you're doing software development or programming, you're pretty much set to go with any Linux distro. Most of the language libraries are pre-installed (like Python, Perl, etc) and the biggest advantage over Windows is you have access to this thing called a Terminal. You can write and compile programs without having to download extra stuff. I know Windows has command prompt, but Linux's terminal totally shits all over it in terms of usability. For example, you can install programs straight from the terminal without having to go to the website and downloading it manually.
This is more of an aesthetic thing, but the font rendering on Linux is nicer than Windows (which uses ClearType I believe). It's quite similar to the gorgeous sub-pixel font rendering you see on Mac displays.
Having said all this, it has its drawbacks. If you're a gamer like me, you'd want to keep both Windows and Linux on your system, so you can dual-boot. Most popular games are released for Windows only (Battlefield, Far Cry, Crysis, you get it). Gaming on Linux is tough, you'll have to fiddle around to get drivers for your graphics card working, and extra features like VSync don't work on the desktop without some tweaking. Also, I keep Windows for photoshopping, since Adobe's creative suite isn't released on Linux.
I realised I began to get a bit technical towards the end lol, hope that was easy to understand.
You can check out a live preview of Ubuntu
right here, you'll get a feel for the desktop environment