This is a moot point. Slackware isn't going anywhere. Currently, there are preparations underway to splice DNA from Ozzy Osbourne and Keith Richards into Patrick so he too will become immortal, and continue to spin Slack forever!
um... for me? Okay...
...and in no particular order either.
I'm sure that, on the linux side, I would prolly end up still using all three of the above the same as I do now, and filling in the slack gap where need be.
On the BSD side, I would end up choosing them for an install the same way I do now, but would prolly use FreeBSD more for desktops, encroaching on territory I now use a lot with Linux.
Solaris is often my first choice in a server operating system, and I usually maintain at least one desktop running Solaris. I'm afraid that Oracle may have killed Solaris, however, with re-instating the licensing fees.
I have the very last shrink wrap version of Solaris to ship under the free license, and right now I'm tippy toeing around the notion that Sun and Solaris might not survive as icons, although I'm seeing Sun branding disappear little by little.
If Oracle isn't very careful, their line of "Oracle Servers" might drive Solaris into the same fate as SCO.