Best OS with GUI for business laptop?

Recently went and purchased a laptop specifically for two things; all things business, and writing any ramblings/stories etc.

I purchased a new Dell, 2.3ghz i3 quad core, 6GB ram, 1TB hard drive (wanted an ssd but was not optional for the price I got it at).

I ideally want to run linux, but I need a GUI and one that actually works properly as I have next to no linux knowledge currently (but want to learn). Infact the only nix knowledge I have is basic SSH.

More to the point it needs to be very secure, I dont want to worry about some Windows 0 day comprimising the passwords to my ltd company web server etc.

I plan to use TrueCrypt too however is it easy to unlock the partition to edit the files and then lock it again or is it strictly for backup usage?

Many thanks.