For me, the surf dictates the board. The board dictates the style. I don't try to ride a fish like a groveler... or a log like a shortboard. It just doesn't feel right, and I'm pretty sure it looks bad, too. I guess that's the most important thing... trying to ride the board the way it's designed to be ridden, taking advantage of it's strengths, and not trying to force it to do something it's not supposed to do.
In smaller and weaker surf, fish and logs should be surfed with flow and grace. These waves don't have much power, so these boards emphasize flow and style.
In medium, snappy surf, grovelers are surfed with quickness, and a more snappy, slashy style, to match the wave.
Performance shortboards should be surfed with power, and in the pocket, matching the power of better surf.
A stepup or semigun is surfed with speed and control, in tune with the speed and almost "slow motion" power that comes with the size.