Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
When you tell someone, "I'm going to buy a car," you usually hear, "Which one?" Ford, Toyota, Mitsubishi, Honda, Saturn? Two-door, four-door, mini-van? And so on.
Likewise, if you say "I want to run Linux," you'll get the same question: Which one? There's no one "Linux" in the same sense that there's no one "car". There are things common among all cars as there are among all Linux distributions: all cars have an engine, and all Linux distributions share the Linux kernel and many of the GNU utilities.
But that's where the similarities begin and end. There are easily hundreds, if not thousands of Linux distributions that are maintained and updated regularly, many of which are tailored for extremely specific needs.
Think I'm kidding about speciialization? There's even a flavor of Linux dedicated to the Asian strategy game Go, called Hikarunix.
Who's to say what's worth running? I've taken about twenty of the most popular and useful distros and grouped them by the way they answer specific user needs.