  We compare the spectrum of the stochastic gravitational wave background
produced in several models of cosmic strings with the common-spectrum process
recently reported by NANOGrav. We discuss theoretical uncertainties in
computing such a background, and show that despite such uncertainties, cosmic
strings remain a good explanation for the potential signal, but the
consequences for cosmic string parameters depend on the model. Superstrings
could also explain the signal, but only in a restricted parameter space where
their network behavior is effectively identical to that of ordinary cosmic
strings.
