The higher, the better. 60 mhz means that the image on your monitor
will be refreshed 60 times a second. At 60 mhz you may notice some
flicker. At higher rates the image will be more "solid" (or clearer as
you noticed.)
The only problem is, that a high refresh rate can "cook" your monitor.
Modern monitors, however, are safe. Check the specs of your monitor!
Remco