The nearest large galaxy to the Milky Way is the Andromeda Galaxy. It is of similar size and is visible in dark skies.
An unbarred spiral galaxy
The galaxy cluster is a group (a cluster) of galaxies. In that light, a galaxy cluster is much larger. Note that galaxies come in different sizes, and so do the clusters. But it is doubtful that even...
An irregular galaxy is a galaxy with no define shape