Ubuntu, without any doubt!
Ray

Linux Mint Debian Edition

Rock solid KANOTIX (debian) is not en the list..... try it and enjoy it!.

Hey...? Don't forget "CentOS", It's my Distro

Arch

Personaly I like Netrunner. I'm currently using version 14.01 - Enigma 2. It is very stable, reliable, comes with many pre-installed apps and looks great! I originally used Ubuntu 9.04, some several years ago, but really preferred KDE. So after many distro hops, I landed on Kubuntu, which I really liked. Hoever, I found Kubuntu was prone to hanging and seemed to need to be restarted a lot more often than I would expect of Linux. So I finaly arrived at Netrunner 'DryLand' a year or two ago and have used Netrunner ever since.
Now if Netrunner was to be released with a Debian core, as a rolling distro, complete with KDE front end... Well, I just couldn't help myself. So my vote, as it stands for now, is for Netrunner.
Thank you for the oportunity to voice my opinion. Cheers, Jim

Linux Mint. You have access to a wide range of tested and hassle-free packages that are available for Ubuntu & Debian, plus that the Cinnamon (or Mate) is much lighter and more elegant than Unity/Gnome. In addition, every time you're in hurry and have to use a set of packages to get your job done (without distracting from what you're doing), you don't have to build up every single package from scratch. It's still customizable. By the way, I realy like WIMP design principle as it's more user friendly and easier for navigation.

Debian Stable

mostly ubuntu and also using slackware

Arch for the freedom it offers its users and its amazing documentation.

For me, it is Mageia. It is only because Mageia is the most just works on my laptop.

Slackware!

Really? Yikes!!

Mayhaps you should take a look at Slack or Arch if you're priority is widest range of choice. Now, that said, you're going to have to work harder to get there from here than putting in a disk and clicking a few mouse clicks to get a working desktop, but from where I sit, building from ground up represents the ultimate in choice. Indeed, it is debatable whether backing out who knows what all got added by automated installer, various dependencies, and tracking down ensuing breakages is in fact far more time consuming that adding in everything that you need/want from a minimal base provided by something like Slack or Arch (or e.g. OpenBSD or FreeBSD). From my experience, I would argue that building from ground up is much less time consuming in the final analysis. At least for those who want it their way. Now, if you're happy as a clam with what that installer gave you... that is another matter. But you indicated you favore widest choice, so.... there you go. My $0.02

1 members found this post helpful.

Erm, but Slackware installs a heck of a lot for the default install so that you don't have to track down dependencies. I'm not knocking it but it differs from dependency-resolving distributions only in that the packages are there from the beginning. Otherwise you're doing your own dependency checking and can just as easily mess up as a package manager could.
I do like Slackware, by the way, but it's a little disingenuous to suggest that a package manager somehow creates breakages that you can't get without dependency management.

This in reply to my post above? Okay, admittedly I haven't installed/used Slack for many, many years now, but last I did (decade ago??) you were pretty much building/compiling everything from ground up. Just to be clear, I wasn't referencing package manager. I was thinking more in terms of what you get from a "default install" and then customizing form there. Thanks for your insights.

P.S.; Yes, I know that Debian installer offer very base, minimalistic install as well, but you need to go to expert mode, no? Anyhow, maybe o.p. was correct after all.... I've got old Debian 1.0 CD's in the pile somewhere but gotten away from Debian in recent years, so not up on the lastest.