What do you use? BSD?
No question Linux wins on (b) given all the corporate backing, but whenever I revisit systems like Buildroot or Yocto I feel the system I am using wins on (a). More likely than not I am just resistant to change and not wanting to invest the effort to master those systems.
Purely subjective, but I suspect the system I devised for myself is simpler and more "stable" in the sense it is less reliant on third parties and thus less brittle. Those qualities are important to me.
Not sure if anyone has mentioned VoidLinux yet in this thread. Probably well worth a look at least as an example if "small and simple" are design goals.
Gentoo and its Portage are IMO really good for distro building, though I would not say it is "small" or "simple". NixOS might also be a good distro builder, from the little I've read about it.
On the same note, I take it your systems are very "I'm using the [whichever]BSD kernel and userland, but this is my own creation" as opposed to stock [whichever]BSD.
A related tangential question:
I've been on the fence about BSD distributions for a really long time, specifically the viability of maintaining them. The few that exist seem to end up forking the entire system, as opposed to just running off with the stock kernel and maybe doing package management differently. That puts huge pressure+responsibility on the person doing the fork.
My question is, are things the way they are because people wanted to fork the kernel for a specific reason and their fork naturally pulled userspace along, or is there a specific reticence toward forking userspaces in the *BSD world?