I use nothing but soap and water on mine, buff with a clean cloth. Mine are darker granite, and they look beautiful years after the fact.
Also, despite prior posts, I use vinegar on mine near the sink as they get hard water spots there, and after doing this periodically for 4+ years, there is no etching, and absolutely no difference between the shine on this area than there is anywhere else on my counters. I don't buy that vinegar (a relatively mild acid) will etch granite (a very hard rock).
ETA:
Before using vinegar, make sure the counter you have is truly GRANITE. If it's marble or other limestone based stone, vinegar most definitely WILL etch this stone and should NEVER be used. Heck, I used to have marble countertops, and even orange juice drops which inadvertently landed on the surface would mar it. I loathed marble in the kitchen or baths for this reason. Too many acidic things being used.
As I say, though, no harm on my true "Rockville White" (black in color) granite.