It really depends on the norms of the organization. What do your peers use? Use similar sign-offs.
However, the sign off line is an excellent opportunity to express gratitude and show a little warmth and good will.
This is especially important as skilled email writers will keep the body of the email very cogent and short. One must get to the point in emails and this doesn’t leave much room for niceties.
A “thank you” might work for this but even better is a note of gratitude for something specific. It demonstrates appreciation to the other person: “BTW, thanks for helping out with xxx yesterday!” You could also express anticipation for whatever the response to the email will be: “So excited to see your TPS reports!” (That sounds like a joke but the point stands).