Now I'm confused. notmuch does tags while mu does not. If you do NOT need tags, then you want mu. That's the one that doesn't have tags. mu using standard IMAP

Now I'm confused. notmuch does tags while mu does not. If you do NOT need tags, then you want mu. That's the one that doesn't have tags. mu using standard IMAP folders means it can interoperate with other mail tools. That's the biggest consideration, I think