So I've been using Slackware now for close to 2 years-ish, and really love it's philosophy. Having that in mind, if I want to "mess around" with BSD on a x86 platform, which BSD should I try out?

Keep in mind that I'm not doing anything particular with it, just want to learn by breaking stuff, and will probably try out different flavors, but I need a starting point of some kind and would like to know what Slackware users favor...

I've run FreeBSD, it is a solid version of BSD. The installer is similar to Slackware.

I like OpenBSD. YMMV

From simplicity and leanness point of view I would vote for NetBSD

My vote goes for FreeBSD as the 1st one to try because you can do 'almost' anything you can in 'Linux'.
I believe you're right, you don't wanna miss anyone. I'd say FreeBSD feels like Gentoo and OpenBSD feels like Slackware (Just my personal view).
cons I found: FreeBSD feels bloated (lots of deps).
Open/Net/BSD no nvidia video driver for me. In the end I was using linux emulation for everything and asked myself what's the point run linux then! But it's fun to play with and they're great for servers.
Here's a nice distro based on Slackware that uses NetBSD's package manager pkgsrc called dracolinux. It's great, but to be honest, I prefer Portage
(Well, I'm using paludis anyway)
Have fun, tell us what you think of them, they're all nice!

I am a big fan of the BSDs. Personally, I enjoy using FreeBSD and OpenBSD. My home gateway/firewall is OpenBSD running off a Compact Flash card on a Soekris 4801 -- cool stuff. Like with anything, try 'em all and see which one you like best.

I think you'll have an easier time with FreeBSD first. I'm with workman in that Open is my favorite but Free would be a good stepping stone to Open.

Thanks everyone, the suggestions have really helped me make up my mind. I think I'll jump right into OpenBSD, since that's what I did with Linux and Slackware, and didn't find the experience too harrowing (quite fun actually).

randomsel, if you haven't already installed OpenBSD 4.2, something to consider is that 4.3 will be out May 1st.

I've used FreeBSD since 2.21 and OpenBSD since 3.0 You'll like any of them and don't forget to read the doc/faq pages

One MAJOR advantage to using SW first: That statement is already ingrained into your brain.....lol

I thought about messing with the BSDs, Open and Free and I am still leaning towards Free. I do have a virtual machine setup running FreeBSD. I'm still not used to how the BSDs take care of partitioning (slices), and I heard that the BSDs use a completely different partitioning sceme which could make it difficult to multiboot, (no doslike disc structure).

The only reason why I am already leaning towards FreeBSD, is that FreeBSD seems a little more lax on drivers. I understand the need for correctness which is the OpenBSD philosophy, but I can't agree with their position with 'binary blobs' such as NVidia drivers. I myself am willing to use a binary driver with no source code in order to get full functionality of my graphics card. I know that some people would like to have source code, but the way I see it, I am not deep enough into mucking around with the actual source code of the system or graphics drivers itself. The only mucking around with source code I ever did, was recompiling of the kernel, but not anything added by my own hands to the source itself. I don't have the aptitude for programming, even though I have taken some programming courses in C++, I just don't have the talent for it.

Another thing about FreeBSD (well, I am now suddenly criticizing here, and I don't mean to, I'm sorry, this doesn't take away my curiousity about the BSDs though). BSDs though might use UFS, they are not compatible with each other as far as I know. UFS would be different in FreeBSD, than in Open, and I doubt OpenBSD uses UFS+2, FreeBSD does. BSD filesystems are not really inline with each other. Also, BSDs, seem to be against any kind of filesystem journaling, though FreeBSD seems to support XFS (experimental) as well as an implemintation of ZFS, but I doubt FreeBSD will ever give the choice of installing onto a ZFS partition. This is also something I found interesting, from wikipedia:

There it is...
So, what made the team at FreeBSD to allow journaling? Is that what UFS+2 is? Because UFS+ is just UFS with soft-updates. And I can't find any mention of this in the documentation, which is a bit outdated. Nothing in the documentation mentions anything about UFS+2 , even though the documentation now is marked as '5.x, 6.x, and 7.x'. Strange..

Anyways, didn't mean to get too far off topic. Like I said before, I am still interested in BSD too, FreeBSD, and want to still work in it.

I use OpenBSD on my laptop and server and I'm loving it.