Re: I use FreeBSD, and for good reason.
I'd probably suggest Devuan, although I use Salix. I generally use Linux just as a Xen dom0 rather than a day to day OS.
I personally use Salix, because I like a fairly minimal Linux. Other people have mentioned Void which sounds interesting but I haven't tried. I haven't tried Devuan, but I have used Debian pre systemd and it's not bad.
Slackware (without additional software) doesn't include dependency tracking when installing software, which is a right pain. It doesn't include Network Manager, which personally I think is a huge bonus.
Salix does include dependency tracking, in fact there's two different ways of installing software. It uses LILO which is a pain on multi disk or multi stage boots (use mbootpack). Easy to install, works quite well.