I think all Linux distributions are wonderful, and I have a special fondness for Debian and Debian derivatives. You can't beat the depth and breadth of the Debian software repositories, which at 18,000 packages and counting are by far the largest of all. Debian's package management system is superb, and it is easy to control what goes on your system- you can go for 100% Free software by simply choosing the repos that contain only Free software, or you can choose non-Free repositories to get things like Nvidia and ATI drivers, Broadcom drivers, and multimedia codecs. Debian supports more hardware platforms than any other distribution. It's rare that you'll ever need to compile a program from source code; it would have to be very new, obscure, or not compiled with the options that you want.
You also have the option of choosing the maturity level of your software: Experimental, Unstable, Testing, or Stable. Hardy souls can even mix-and-match, though this can lead to dependency conflicts. A well-maintained Debian system can be upgraded indefinitely without ever requiring a reinstallation.
So if Debian is so wonderful, why isn't it more popular? Actually it is popular, and has been almost from its inception in 1993. It doesn't have a flashy turbo-charged marketing engine behind it like the Ubuntu family, but it's consistently in the top 10 on Distrowatch, and keeps chugging along year after year, and keeps spawning good derivatives like Ubuntu, Mint, Mepis, Knoppix, Dreamlinux, and many more.