  Aims. With the aim of performing a suitable comparison of the internal
process of galactic bars with respect to the external effect of interactions on
driving gas toward the inner most region of the galaxies, we explored the
efficiency of both mechanisms on central nuclear activity in active galactic
nuclei (AGN) in spiral galaxies. Methods. We selected samples of barred AGN and
active objects residing in pair systems, derived from the Sloan Digital Sky
Survey (SDSS). In order to carry out a reliable comparison of both samples
(AGNs in barred hosts in isolation and in galaxy pairs), we selected spiral AGN
galaxies with similar distributions of redshift, magnitude, stellar mass, color
and stellar age population from both catalogs. With the goal of providing an
appropriate quantification of the influence of bars and interactions on nuclear
activity, we also constructed a suitable control sample of unbarred spiral AGNs
with similar host properties than the other two samples. Results. We found that
barred AGNs show an excess of nuclear activity (as derived from the
$Lum[OIII]$) and accretion rate ($\cal R$) with respect to AGN in pairs. In
addition, both samples show an excess of high values of $Lum[OIII]$ and $\cal
R$ with respect to unbarred AGNs in the control sample. We also found that the
fractions of AGNs with powerful nuclear activity and high accretion rates
increase toward more massive hosts with bluer colors and younger stellar
populations. Moreover, AGNs with bars exhibit a higher fraction of galaxies
with powerful $Lum[OIII]$ and efficient $\cal R$ with respect to AGNs
inhabiting pair systems. Regarding to AGN belonging to pair systems, we found
that the central nuclear activity is remarkably dependent on the galaxy pair
companion features.
