I have a custom field that is a lookup to the standard parent field to use in place of it for a functionality on the Account object. I now have a requirment for the standard parent field to have the same value as the custom lookup field whenever it is edited. Would it be easier to create logic with a class and trigger or process builder?
Process Builder would be a lot simpler in this case, although it may have unintended side effects during mass updates, so you will want to test your logic carefully with bulk updates to make sure you don't run in to any problems.
I would say use the process builder, however, it all depends on what you're more comfortable with, I personally would use a process builder as its such a simple process.