I honestly find black borders really distracting, as they are the same colour as the cell values. The built-in grey borders are ideal for me. And often when reading a row across, I'll select it.
I only use them for tables going in a powerpoint or email tbf and never apply a complete grid of them, just borders around important rows or columns to call out what to focus on, simliar to make the row bold or italic
I honestly find black borders really distracting, as they are the same colour as the cell values. The built-in grey borders are ideal for me. And often when reading a row across, I'll select it.