  We study ultraslow diffusion processes with logarithmic mean squared
displacement (MSD) $\langle x^2(t)\rangle\simeq\log^{\gamma}t$. Comparison of
annealed continuous time random walks (CTRWs) with logarithmic waiting time
distribution $\psi(\tau)\simeq1/(\tau\log^{1+\gamma}\tau)$ and Sinai diffusion
in quenched random landscapes shows striking similarities, despite their very
different physical nature. In particular, they exhibit a weakly non-ergodic
disparity of the time and ensemble averaged MSDs. Remarkably, for the CTRW we
observe that the fluctuations of time averages become universal with an
exponential suppression of mobile trajectories. We discuss the fundamental
connection between the Golosov localization effect and non-ergodicity in the
sense of the disparity between ensemble and time averaged MSD.
