I'm a "Best wishes," for more important / formal emails, and an "All the best," otherwise. Or I'll just write my name if the email is one line / very casual.
Rarely get to use "Many thanks," as it seems a bit aggressive to me to thank someone while making the request - I don't take it that way when I see it, but I feel awkward writing it. If I needed to thank someone in advance I would prefer to include e.g. "Many thanks in advance for any help you can provide with this" as a closing sentence as that feels more sincere to me when I'm sat there overthinking how to write emails (
). If I'm sending a specific thank you note I'll often sign off "Thanks again," though to really ram that politeness home.