(Xu-/Lu-/U)buntu is great for beginners. It just works out of the box, even with more "complicated" setups, since it uses proprietary drivers nearly "by-default". RAID-Cards should be no problem, and even software-RAID's should work fine, after you RTFM'd in the ubuntu wiki Although I guess, canonical(The guys behind Ubuntu) are messing their system up quite badly atm... (mir/xmir, Unity, They spy-search-thing, ...)
If you're willing to invest some time, use Debian(As live system GRML). It's not as easy as *buntu, but a great OS!
I wouldn't recommend any of these more "exotic" distros like Pear OS and stuff, since you won't find much support for those anywhere.
For gaming, you should install PlayOnLinux & Steam.
For more productive work, you could use LibreOffice. It's a fork("clone") of OpenOffice, but more Libre! (It's basically the same...), and maybe geany if you're into coding/LaTeX/a good GUI text editor.