I really like xv6 for its simplicity and restricted scope. It feels like a better Minix in the sense of being a codebase intended for university coursework. If your goal is learning the very basics of what an OS does, xv6 is a good place to start. ToaruOS can cover the same ground - of course there's paging and IPC and threads - but I don't have a cache of PDFs sitting around describing it, and there's no intentionally missing bits waiting for a student to fill them in for homework. If xv6 is "Operating Systems 101", then ToaruOS is a 300-level seminar/workshop.

My intended audience is hobbyists who are looking for a reference for writing their own OS - the sort of people we often find on osdev.org, or the #osdev channel on Libera, who have stumbled through an old tutorial on x86 bring-up and want some example of how "the next steps" work.

Also interested in this question. Never finished the MIT os course utilizing xv6.