What's more common? Re / Im or Fraktur-R / Fraktur-I for real / imaginary part?

I lean towards readability and I find $\operatorname{Re}z$ and $\operatorname{Im}z$ unambiguously clear.

I prefer the fraktur notation. Firstly, it looks much more elegant. Secondly, it is unambiguous (for instance, Re is often used for Reynolds number).