Mostly I use Redfield's and have had good luck with them. Leupolds are top of the line. One's I would look into are the Millett's. I've used their rings and bases a couple times.They appear to be as good as the Redfield's for less money.I've never tried Leupold's but wouldn't hesitate using them.If you stick with any of the three mentioned you'll do fine. I would stay away from the cheaper mounts.
I prefer steel mounts and rings.

Ruger Redhawk