EVERYONE has their own choices and opinions about which Linux Distro is best. This is simply another HUMBLE OPINION on which Linux Distribution to decide upon. There are literally thousands to choose, I have tried tens of tens, and these are my choice recommendations for a Linux Desktop.
COMPLETE NOOB: (or tired of Ubuntu and want a little more class)
If you are completely new or very novice, I suggest Linux Mint. Mint is easier and a bit more complete than Ubuntu, as it is based from the Ubuntu Distributions with added features and usability. Since it is Ubuntu based, expect updates slightly behind Ubuntu's releases, but the fine-tuning is already there for you.
AVERAGE JOE: (Today's most popular distribution)
If you have a shallow Linux background, you can start with Ubuntu. It's where I learned most of my experience in my second coming into Linux and I recommend it as a great way to start the fun. Ubuntu is highly modified and much easier than base distributions. It is Debian-based with many added features to make using Linux as an every-day desktop very easy.
If you've learned the basics and then some, and are tired of Ubuntu's random breakages, bugs, or user interfaces, then Debian is for you. It is King. There are several branches: Stable, Testing, and Unstable. For a good balance between stable and cutting edge, I always choose testing. There are usually ways to install cutting edge software within Debian regardless of which branch you use. However, I list this under "experienced hacker" with reason.
LIGHT IN THE FEET:
If all of the above Distros are just too power hungry, try CrunchBang. Previously Ubuntu-based and now Debian-based it's lightweight and quick as lightning. Using CrunchBang makes you the envy of all your dorky friends and upgrades you to an elite class of nerd.
The above mentioned Distros are ALL Debian. If you know commands in one, you know them in the others. The easy ones have done a great deal to lessen the pain such as automatically adding users to the sudoers file and adding paths to environment variable to make command line action easier. That and a hole bunch of eye-candy and applications give them modern pizazz. You could theoretically start with Debian and make your own super-distro. But why do what others have spent millions of dollars doing for you.
The real world work-force tends to use Red Hat Enterprise Linux. But for you and me, we're CHEAP. CentOS is binary compatible, if not equivalent. Updates are generally only a few weeks slower than the official Red Hat Enterprise distribution. If you need a solid, stable, commercial grade system, this is it.
Debian is a highly popular and extremely stable enterprise ready distribution. Be sure to use the stable branch of course.
I still like to distro hop. Some very interesting Distros I've come to enjoy and keep the newset copies of include Slitaz and TinyCore. Stick them in just about any computer boot from CD and you're running linux without even installing. Yes, most distros are LiveCD's lately, but these are super small and super quick. Burn a business-card CD and keep it in your wallet to show your family, friends, or boss just how cool you really are.