I've had both RST and Judy forks on 2 of my bikes... Their effectiveness depends on your purpose - will you ride casual or serious race? If you want to race, just upgrade the fork - there are many available from Fox, Marzocchi, Rock Shox, Manitou... I've had no major problem with either the RST or Judy fork but I have upgraded to save weight on my bike ('01 Giant RinconSE)

Looks like both brands are similar - go with whatever has the best geometry for your body and fits your wallet. Always sit on a bike before you buy it!