Both are correct. 'Take a piece of paper' is more of a polite request.

I would use either if I am providing the paper and the people I am speaking to are supposed to take one. However, I would say “get out a piece of paper” or “take out a piece of paper” if I wanted the people to use their own paper - for example if they had a notebook and I wanted them to tear a piece out. It’s a very subtle difference