Depends on your meta-ethical framework. If you’re a consequentialist, then you should always choose the option that leads to less evil being done. Same if you’re a utilitarian.

If you hold to a Kantian value-based framework, like the action itself holds the primary moral goodness or evil in its own nature, then choose the action that itself is less evil.

There are many other frameworks. It also depends on what you think happens in the case of something like voting. Some people see participation in any sense as a sort of tacit agreement or endorsement of the system as a whole. So by casting any vote, even one of protest, you are legitimizing the system as a whole.

Others see voting as a mere means to an end, and thus, is justified if the outcome is better than not voting would be. Some see it as purely neutral, like a tool that can be used for good or bad.

Still, others see it as an inherently good thing, and view abstaining from the act of voting as a moral wrong, because it is a willing act of self-sabotage of the moral interests of the greater good, or sometimes as a violation of the social contract.

There are many other positions and considerations. Basically…it’s complicated.