[dontJudge]

Both. Tabs for indents. Spaces for alignments after the indent level is reached.

Everyone can view code with their preferred indent width. Perfect solution with no flaws or drawbacks. Maybe 1 drawback, it requires advanced tooling (emacs smart-tabs-mode) to automatically handle the indentation/alignment.

Indent width is a visual effect. Mandating an indent width with hard spaces is like mandating the color scheme.