We are having our red oak hardwood floors refinished. I do not like the look of the grain in them, so I am wondering what would be the best way to stain them to minimize the look. Would going darker and water popping them help? Or would a medium stain color be best? Thank you.

White stains tend to mute the grain. Water popping will give you a more even color. Pigment type stains will give more even color.
Thats why the white stains mute the grain, they are made with white pigment.
Try the Zar stains that are pigmented.