Void with glibc "just works" in the way that ubuntu is supposed to. It's amazing. I intend to switch to OpenBSD, but I'm no good at porting shit, so it's going to take some doing.
OpenBSD or Alpine/anything with musl will have you struggling to build any programs that aren't in the package manager. Just about everything will be at least slightly broken if the devs aren't themselves OpenBSD users. Things will break when you git-pull, and these are often problems that nobody cares about but you. Still, it's worth fixing these things because musl and OpenBSD are otherwise objectively better than glibc/Linux.
Alpine seemed to use the least amount of memory under my normal load, probably because of busybox. I liked busybox; it seemed to be a good logical reduction of redundancy in the tools. I don't remember the details, but it impressed me with its parsimony and low overhead instead of aggravating me with needless breakage.
I liked OpenBSD's approach, too: the system seems intent on encouraging you to actually read the manpages by eliminating a lot of the `--help` options. You learn more that way. I was curious if OpenBSD supports busybox in some way:
>busybox is a big pile of poo and openbsd does not do what busybox does. but you can probably compare the busybox concept with our crunched install images (see crunchgen(1)), many programs are linked into one single binary to get a very small system.
kek
Alpine's "minimalism" comes too much from being half-baked, imo. The package manager downgraded python to install something, which broke a bunch of other shit, and I couldn't undo very easily. Nothing like that happened on Void or OpenBSD. Would not recommend.
Nor is OpenBSD all smiles and sunshine: it, for example, offers some sort of mk-tmpfs tool despite "tmpfs" not being supported. That's not to say you can't have a ramdisk, though— you just have to use a different, apparently identical tool under a different name. Just some stupid shit you'll have to trip over and spend time on.
I've heard good things about OpenBSD's security design, which is why I ultimately want to stick with that. There are very interesting talks that go into details. Also, pf > iptables.
>Plan9
Never tried. Would like more information.
<Haiku
This probably isn't even "minimal" but I tried it and the installer failed to boot properly. Hung on a loading screen. It's a shame, too; it seemed comfy.
<Kolibrios
Great in theory: just, like, write everything in fasm, bro. You can use C, too, I'm told. In that way, you figure it's even more poz-proof than OpenBSD. In practice I'd rather have the same thing (ie, an OS in ASM that fits on a floppy, etc) pretending to be DOS (single process and all) instead of what kolibrios seems to want to be: Win95. I mean it's a meme OS to begin with, but where's my goddamn bash shell?