I'm gonna go ahead and chime in here real quick. I already said my favorite Linux distros, but this Package Manager stuff is something I have an interest in, so with the last page or so being almost all that, I read through them.
First, Slackware and BSD are actually pretty similar. In fact, if you pay for the actual FreeBSD and Slackware CD or DVD sets, the packaging is even almost identical.
Years ago when 6.0 was the newest RELEASE, I had been in college for Computer Science, and I had gotten my check from the school I was going to, to help pay for things I needed. Well, that particular year, I'd been on Honor Roll, and I got a pretty good sized check, and I decided I'd use a good chunk of it, to catch up on my BSD stuff, so I started looking around for what I wanted. I went to the FreeBSD Mall, and the Slackware store.
I ordered basically everything from the FreeBSD Mall; When I got a phone call for a Confirmation on some info, I remember the girl asking exactly what I ordered, and when I finished telling her, she was pretty shocked at how much money I'd spent. I basically ordered one of everything I could.
I got EVERY book they sold except for The Complete FreeBSD 3rd Edition because I already owned that one, and instead got the O'Reilly version, and then The FreeBSD Handbook, both the second Edition, and both books from third, "Teach Yourself FreeBSD in 24 hours", a FreeBSD 6.0 CD set, which I ended up getting two of those because a book came with the first disc of it as well, so I kept both of the CDs, and then I also got the FreeBSD Mouse pad, which, even though this was a while ago, is what I'm using right now, and the Stickers I got a bunch of, and the Case plates, and the Tee Shirt I'd wanted, and Boxers, everything. And of course; "20 Years of Berkeley Unix" on DVD!!!! (I HIGHLY HIGHLY HIGHLY Recommend ANYONE here, to order this. It's a talk by Marshall Kirk McKusick, who to me, is a Legend, and incredibly funny too. I have watched this thing probably 400 times or more, and I still love it, order it !! You can get it from his web site, but back then I saw it on the BSD Mall site).
That's not all I ordered, but it gives you an idea of how big of an order it was lol. I even spent the extra to over night it. Then, I went to the Slackware store, got the second Edition of Slackware Essentials, the 4 CD set of.... I can't remember if that was 10 or 10.2, but one of them; And then I got the Slackware basic tee shirt, Mouse Pad, a couple of the Case Plates, and, a few other things.
I couldn't over night this one, so I got second day shipping.
Now, about 12 hours or so later, I noticed a package on the Porch. I could see it was from the "FreeBSD Mall" so I grabbed it and brought it in, and it was HUGE. I knew I'd ordered a lot, but I didn't know it was THAT much.
Then I opened it up and it made sense; Inside was all the stuff I'd ordered from the FreeBSD Mall, AND everything from the Slackware store! All in the same box. Then it hit me; I'd already realized that the Official CD-ROM Sets from FreeBSD and Slackware looked A LOT alike, but then I checked my first edition of Slackware Essentials; Sure enough, there was a BSDi logo on the back of the book.
So, long story short, if you order stuff from both stores, you're probably going to get it at the same time, in the same box. I was told by someone who works for the FreeBSD Mall that they actually do in fact do the Slackware store, as they like Pat, and Slackware.
I also got Free Sticker from BSDMall once because another order was having problems and got VERY delayed. I was NOT rude to them about it, I was understanding, but DID tell them that I wasn't exactly happy about it, and because I made my point in a more laid back not freaked out way I ended up with like a BUNCH of FreeBSD and generic "BSD" stickers which literally cover my Laptop.
Actually, BSDMall, MAY be where I got the DVD of Kirk. Either way it's great so buy that!
And also, if you don't know since I'm on the topic; If you go to Kirk's Web site, and check out the stuff you can buy, not only can you get the DVD, but, you can get the CSRG CD set! THAT is what I'm currently aiming at. I REALLY want it. I mean the Historical aspect alone is cool.
Anyway, Slackware and BSD seem pretty close for the most part, and again, because Slackware doesn't do their mods like a lot of other distros do, you really aren't screwed as on person said, if Slackware went under. I mean you could just as easily build the Packages yourself, and do it all yourself, as they aren't modified anyway.
Personally I've used quite a few Package Managers, and the ones I liked best for all around installation, and removing, were FreeBSD's, SuSE Linux (Using Yast, or YAst2 if you have X loaded) and Debian of course.