there is no such thing really as a "good refresh rate" the best refresh rate is whatever your monitor's highest refresh rate is. and that varies with resolution, my monitor is 17" and my highest refresh rate at 1280 by 1024 is 60hz, yet at 1024 by 786 my refresh rate can reach 85hz.
so just set your refreshrate to the highest for each resolution if you are using the nvidia refresh rate fix
I (of course) agree with Qumahlin, but would like to add that the higher refresh rates obviously look better. Lower than 65-70 you'll notice a flickering (esp. under flourescent lights) that is annoying and causes fatigue (so I've heard). BUT, setting it too high can damage the monitor or at least shorten it's life substantially.
ScriptAsylum is right. although the flickering is a thing of the past unless you use a REALLY old monitor, my normal refresh is 1280 by 1024 at 60hz.
As for damage to the monitor N-E-V-E-R manually set a refresh rate higher then your monitor's maximum, most monitors nowadays will not let you do this anyone, they will automatically revert to the working on or you'll get a black screen with a box that says frequency out of range.
My friend set his monitor a few years ago to a high refresh rate which it didn't support and it wasn't longer then 2 days before the monitor fried!