A huge volcanic eruption can cover the atmosphere in ash and end the life on Earth as we know it.

In reality, Yellow Stone geyser (which is technically a volcano) can completely destroy half to three quarters of the continental United States. Parts of Canada and Mexico. While and earthquake has yet to destroy a whole city yet.

The others already argued this side well but I'll just phrase it as a volcano impacts land, sea, and air not only around it but globally, whereas an earthquake, even if it's a very big one, doesn't really have the same global impact.

Both are pretty powerful but earthquakes tend to be more of a local disaster where as a volcano can cause world wide effects.

This of course hugely depends on whether the volcano or earthquake is near to any densely populated areas.

Whilst earthquakes can topple buildings, cause avalanches, landslides and tsunamis, and cause cracks to open up in the ground, they are destructive mainly to manmade objects rather than nature.

A volcano has the potential to blot out the sun with ash. Pyroclastic flows are incredibly dangerous and destructive, as are lahars. Volcanoes are more likely to kill plants, animals and people who are nearby, as most deaths from earthquakes result from something falling on a person.

Volcanoes have caused major extinction event in our planet's history (see the Permian extinction for example, it was very bad) Earthquakes haven't done this as far as I know.

Note, earthquakes and volcanic eruptions can cause one another, so their not mutually exclusive events.