My vote would have to be for all four (which isn't available, so I didn't vote). I can't pick one over the other. Prior to Slackware I tried RedHat, Debian, and Mandrake. None of them were able to achieve all four of your choices, as Slackware does quite well.

I went for stability, cause Pat, unlike Sisyphus, keeps pushing Slack to a higher plane without it rolling back.

I voted simplicity. I believe that, to varying degrees, the other three are caused by this one. I like the simplicity because it makes seeing, understanding, and modifying each piece of the distro a straightforward and well-documented process. You can do it the Slackware way (which is great), but it's easy to change things to "your" way if you want or need. Not to mention there's less overhead as a result of cutting out all the config tools

Stability would have to be number one though. After all, that what made me leave winblows.

I like slackware because it assumes I know what I'm doing. Windows assumes I don't and I am sick of patronising, we know what's best for you messages. If you look up 'advanced' topics in help there are things like how to change the font size. Slackware invites you to mess around under the hood, recompile the kernel, write your own scripts and programs, choose your window manager etc. And it doesn't try to 'enhance your linux experience' or install things behind your back.

edit: Oh yeah I voted for simplicity.

There should definitely be an option E, all the above.

Slackware is So, So Sexy!

I would vote for all of the above, but simplicity is what drew me to slack, I was looking for a more challenging distro one day, and I decided to try Gentoo. Gentoo was the most confusing distro I have ever tried, portage made no sense to me, all these ebuilds and crap like that, so I decided to go with Slackware, because I use to mess around with the Slax livecd alot and so I downloaded the 2 install cds and installed it, right of the bat I was impressed with the speed and efficiency of the installer, it had no bloat, and was simple s possible while getting the job done. Then when the first boot came around, it ran so fast it blew my socks off. I was so impressed I stuck with it.

All of them. Mostly simplicity...

Like other people have said. Slackware assumes that you know what you are doing. Besides when I could choose between red hat and Slackware I chose slackware because it looked most like the SLS 'distribution' I was used to.

Slackware, because I don't want 25 different levels of startup scripts and configuration files.
Slackware, because I *DO* not what I'm doing.
Slackware, when I don't wish to be bogged down by all kinds of "helpful" automation.
Slackware, because I want the computer to EXACTLY what I tell it to do.

Slackware (or Slamd64) is easy to maintain and understand (cleaner) and is also faster than distributions like Redhat or Suse (I'm using those two at work).

Slamd64 11.0 was ~12% faster in long complex calculations than Suse 10.2, but it scared my boss, so he picked out the more friendly looking Suse to run our calculations on ...

(this is custom kernel vs Suse stock kernel, and just a few essential daemons running in Slamd64)

Simplicity is the major reason for me. It facilitates the other three S's of this poll. It also facilitates learning Linux.

I like Slackware because of the Support.

If I have a problem, I can come here and get an almost instantaneous and useful (or at least empathic) response. Some of the other distros (especially those that cover up behind-the-scenes stuff) have users that don't even know what their own machine does.

I don't know about "simplicity" of use, but it is definitely Stable and Secure.

I chose stability.

When distro's say they do things "automagically" I get a vision of witchcraft. Nice if it's used for good, but it is so easy to make mistakes if you write/edit automagic scripts...

But the main reason I keep using slack, even when people say things like "what decent distro still runs 2.4 kernels??" (slack 11.0 does).
The main reason is it is extremely stable. I once saw a win machine giving an error on the login prompt, when I maked a joke about it, a guy said to me "My Ubuntu does that sometimes to, you know".
When programs start to crash randomly on slackware, that's a sign somethings really wrong, on some distros that's a sign that says "time to reboot"

The only distro except slack that impressed me was Kubuntu, because it really was easy to use the config GUI. I formatted that partition when the taskbar kept crashing, and the only advise I got was "reinstall".

Yea, that's a big one also. And if you like to hunt for your own answers, the vanilla-nes of Slack helps a lot (specially in Gentoo wiki).