I don't really have a 2nd favorite OS, just other operating systems that I enjoy using equally. For now my choice OS's are: Slackware, Windows XP, Knoppix, and Mac OS X.

My favourite is FreeBSD then Arch, I don't use Slackware anymore. However I learnt most of what I know about Linux on Slackware so I will always look on it with a certain fondness (I still read the changelog from time to time and I'm still subscribed to the Slackware Security ML, lol).

If I find myself with more time in the future or suddenly have the urge to maintain a few tens of packages myself outside of the official repository I'll come back to Slackware.

I thought I'd give Plan 9 From Bell Labs a mention, but only because Glenda the Space Bunny is my favourite OS mascot

I voted for windows because of the better gaming experience.
Plus when you're on a budget & can only get crappy wireless usb dongles which work only on windows...well....(don't start on ndiswrapper, I've been there since v1.1 release.)

Ive yet to try LFS but it definently sounds like something i would like, but out of the choices, i chose freebsd.

Which other? My Slackware-based live-cd, of course!

Besides Slack? Definitely Arch. Love pacman!!

Oh my god That bunny gives me nightmares :P

*Update: Sun Jul 30 09:33:00 EEST 2006*

Seems like so far FBSD is the leader with nearly 19% of the votes followed by Windows [~ 10%] and a close tie between Arch and *buntu [~ 9%]. [haven't mentioned the "*other" polls]. But I saw quite a lot like LFS and Zenwalk. I'm glad [at least so far] this thread hasn't turned into a flame war. I hope still more people will vote and add post a comment [70 so far]. Thanks to everybody who replied/voted so far

openbsd

the same purity as slackware.

Slackware for a Linux distro. When I know enough I want to
build LFS like druuna -- I'm not knowledgable enough today.

Windows XP Pro because as cwwilson721 said, It Just Works (TM)
and all the software which I need to do actual work with is
written for Windoze only; and there's no OSS substitute.

nothing comes close to running slack, when you need to do work. 1 more Linux that I am equally aquainted with is Red Hat Linux including its enterprise editions. Haven't got to use Fedora till now. I incidently have a copy of KNoppix CD sitting in my desk now. My laptop here dual boots with slack and xp. I have two computer's with me at home, one runs slack, the other i don't know what i put in there, i rarely use it for except watching tv. I have tried Gentoo, its configuratibility is damn nice, but I sometimes think its over kill. i downloaded arch a month ago, haven't tried it yet though.

After Slackware I'd say Mac OS X and Windows. I also like Ubuntu 6.06 because apt-get is amazing:-)
When I get home from vacation I'm going to take another run at FreeBSD, the last time I ran FreeBSD was the 5.2 version, I like the look of 6.1:-)
I'm posting this from a Windows box.........oh, the horror:-)

SUSE with Smart as a package manager is my #2.

I'm still working on getting a working installation of Slackware on my hardware. But, the Slackware philosphy matches mine. I have purchased a subscription that begins with 11.0, and it will become my main distro with SUSE as a backup.

Ah .. Mac .. another thing I really should have included in the poll. This is what you get from a user who hasn't touched anything other than Linux/BSD for a couple of years

Arch seems really quite low on the polls.. certainly lower than I would have expected. I haven't tried Arch myself but from their wiki:

P.S.: I don't really buy the "more robust package management" part, but like I said, haven't tried it.

P.P.S.: Please don't use the above quote to start a flame war against Arch/Arch Users/Arch Wiki

I forgot to mention .. I myself, the OP, voted for *buntu. It's probably somewhere at the opposite end of Slackware, but I liked it's usability, and the fact that I managed to obtain a nice, clean, dark Gnome desktop really appealed to me. My next choice would definitely be FreeBSD.

IMO most guys who use Slackware eventually aren't depending on a
package manager. They compile from source and use Checkinstall,
makepkg, SlackBuild scripts or similar to make their own packages
for things not included in the distro; or later versions of software.

Never used a Mac, but tired Mac OS-X x86 -- it crashed quite a bit.
I tried to update it, but it was quite slow and when the screensaver
kicked in the entire system locked. Upon reboot, it was corrupted.