But the example with multiple selectors and & at the start is unclear due to the precedence of the @nest operator over the comma:

    /* @nest always */
    @nest & + .baz,
    &.qux {
      color: red;
    }

It's clearer perhaps with different nesting, but that's fragile and a pain:

    /* @nest always */
    @nest & + .baz,
          &.qux {
      color: red;
    }

At least with option 1 you only end up with this issue in the uncommon case of multiple selectors and a non-leading &.

    /* @nest */
    & + .baz,
    &.qux {
      color: red;
    }