Topic says it all. What distro do you use and why?
I use Gentoo because of portage, it's package management tool. Dependancy hell is pretty much eliminated. You can run 2 or more different versions of many packages, such as gtk, gcc, etc. It has an excellent forum community where people can usually find their answer (note I say "usually"). The most important aspect is optimization, per system and per package. The logo is neat (Larry the Cow). Last but not least, Gentoo's are the cutest animals on earth. They are a breed of penguins.