Differences from dpm and dsm for devel module for debugging objects?
From the documentation:

Legacy function that was poorly named.
Use dpm() instead, since the 'p' maps to 'print_r'.
Code
function dsm($input, $name = NULL) {
  return dpm($input, $name);
}


So there is no real difference, except the function you are using is left there for developers that failed to switch when it was renamed.