  This is the second paper of a series devoted to study the stellar content of
early-type galaxies. The goal of the series is to set constraints on the
evolutionary status of these objects. We use a new set of models which include
an improved stellar library (MILES) to derive simple stellar population
(SSP)-equivalent parameters in a sample of 98 early-type galaxies. The sample
contains galaxies in the field, poor groups, and galaxies in the Virgo and Coma
clusters.We find that low-density environment galaxies span a larger range in
SSP age and metallicity than their counterparts in high density environments,
with a tendency for lower sigma galaxies to be younger. Early-type galaxies in
low-density environments appear on average ~1.5 Gyr younger and more metal rich
than their counterparts in high density environments. The sample of low-density
environment galaxies shows an age metallicity relation in which younger
galaxies are found to be more metal rich, but only when metallicity is measured
with a Fe-sensitive index. Conversely, there is no age-metallicity relation
when the metallicity is measured with a Mg sensitive index. The
mass-metallicity relation is only appreciable for the low-density environment
galaxies when the metallicity is measured with a Mg-sensitive index and not
when the metallicity is measured with other indicators. On the contrary, this
relation exists for the high-density environment galaxies independently of the
indicator used to measure the metallicity. This suggests a dependence of the
mass-metallicity relation on the environment of the galaxies. Our data favour a
scenario in which galaxies in low density environments have suffered a more
extended star formation history than the galaxies in the Coma cluster, which
appear to host more homogenous stellar populations.
