Answer:
It is sometimes difficult to tell; our judgment of the size of another galaxy is greatly influenced by the DISTANCE to the other galaxy, and the distance to another galaxy is sometimes tough to know with any precision. Astronomers have revised their distance estimates several times, and we cannot know that we're right THIS time.
But based on what we currently believe to be true, the Milky Way is a larger-than-average galaxy similar to the Andromeda galaxy.