Both is for breaking up stones. I would think it is a matter of preference. People are happy with both products.
I use chanca piedra. According to Ask Andreas Moritz you can take it for months. He advised one person to do it for 2 months and then take a break for a week. I tried GCG twice but I did not feel well on the herbs, I should say noone else has ever mentioned that, just me. Most people love it.