Debian Linux for server (stable, tested).
Rant: Few years ago the state of yum based distros was very bad and at that time Ubuntu came and was instantly favoured. Right now rpm based distros are in much better shape and deserves a shot. About pkg-management -- I find apt clumsy for example you need to apt-cache search/list, but to install do apt-get install; I like yum (search/install etc. just one tool) and rpm a lot.
A user friendly version of Arch. It includes a graphic package manager - which seems to be discouraged by the main Arch distro looking at their wiki (they want you to learn and understand pacman). The fact is sometimes I want a graphical package manager to make searching easier and I don't know the exact name of the package I am looking for. Other times when I do know the details it is easier to use the command line. Having the choice is good.
None of them are perfect, but my experience with Ubuntu is that it is hands down, the most desktop-friendly distro out there.
On the other hand, the "RPM hell" that is rumored to be gone in RPM-based distros, is still alive and well. I had a STABLE server-based distro warn me that packages were broken, and there were unresolvable dependencies. This was with a very vanilla install, and no extra repos. Needless to say, it scared me away from RPM-based distros for the foreseeable future.
Is Ubuntu problem-free? Certainly not. However, when I have encountered the occasional issue, there have been workarounds.
The other thing is... if someone is making a Linux version of their app, everyone and their uncle is providing .deb packages. There's a LOT of momentum behind it. So... if I'm going to go off the beaten path of OS X and (heaven forbid) Windows... Ubuntu is the most painless.
Another reason I like Ubuntu so much is its polish. It looks more polished than any distro I've used, to date.
I hear they may do some patching with their fonts, and some other magic under the hood.
I like Arch Linux, as well. If I could get Ubuntu's polish on Arch, it would be a perfect world. :)
I bought it the month before 911. In 2004 it was stolen and pawned and I had to take the pawn broker to court to get it back. When we were still on 802.11b my son used it with Windows 2k (rather than its original ME) and a PCMCIA wireless card. In 2009, I replaced the voltage regulator for the screen with one from eBay. Then it sat dormant for a few years after the Wireless network was upgraded.
A couple of years ago, I tried installing Linux and paid the dumbtax when I reformatted the hard disk. Then recently I pulled it apart, stuck in the BroadCom daughter card and 40gig hard disk salvaged from another laptop and after more work than I care to admit got it up and running and productive again.
I've got Emacs and MITscheme for fun. Node runs too. There's SSH to the big box [CentOS 6.5] for anything else. What more could I want?
Well ok, a couple of 256meg SODIMS and a PCMCIA ethernet card would be nice.
Netbook: Ubuntu LTS (12.10 I think). Thunderbird. Everything works (except, oddly, google chrome doesn't play video worth a crap- may be the old specs).
Servers: Debian Squeeze. Solid server distro.
CentOS on servers. Rock solid, long support.
I had an Ubuntu phase when it was first released. Even helped 2 companies standardize on it while moving developers off windows machines to Linux. But ditched it for personal use when Fedora 7 came out.
The only other distro that interests me is Arch. It's definitely the tweakers distro, and if I were younger and had more time to tinker with Linux I'd run it on my desktop.
I guess the main reason why is familiarity - 17 years with RPM based distros.
Note: Main area it is lacking is the "just works without setup"; it does not compete with Ubuntu/Mint/etc on that front.
Full disclosure: I'm the founder and lead developer.
Linux from Scratch - I am a masochist
I am just super glad after all these years we are all able to download and use (for free mostly) such an excellent OS.
Servers - Debian ( Stable, Secure, Well documented with good tutorials )
Maybe this will happen if it's going to be based off of 14.04.