  Since cosmic-microwave-background (CMB) and large-scale-structure (LSS) data
will shortly improve dramatically with the Microwave Anisotropy Probe (MAP) and
Planck Surveyor, and the Anglo-Australian 2-Degree Field (2dF) and Sloan
Digital Sky Survey (SDSS), respectively, it is timely to ask which of the CMB
or LSS will provide a better probe of primordial non-gaussianity. In this paper
we consider this question, using the bispectrum as a discriminating statistic.
We consider several non-gaussian models and find that in each case the CMB will
provide a better probe of primordial non-gaussianity. Since the bispectrum is
the lowest-order statistic expected to arise in a generic non-gaussian model,
our results suggest that if CMB maps appear gaussian, then apparent deviations
from gaussian initial conditions in galaxy surveys can be attributed with
confidence to the effects of biasing. We demonstrate this precisely for the
spatial bispectrum induced by local non-linear biasing.
