1: … is off topic and should be migrated to a site for which there is a migration path?
Vote to close as off-topic as "belongs on another site".
2: … is off topic and should be migrated to a site not listed in the vote-to-close dialog?
Vote to close as off-topic and flag for ♦ moderator attention using the free-text box.
This ensures that even if we don't believe the migration is warranted that you will at least still be helping to close an off-topic question.
Make sure the question is off-topic here, on-topic there and good quality before taking action – if it's not all three of these things we won't even consider migration.
3: … is off topic and should not be migrated?
Vote to close as off-topic as "off-topic".
4: … should be closed for some other reason?
Vote to close using the relevant close reason.
If none of the reasons fit then consider if it really does need closing, and maybe flag for a ♦ using the free-text flag if you believe there is a case for doing so.
5: … requires a moderator action other than closing, such as deletion?
If it's something the community can do first (edit to fix problems, flag spam, close, etc) then that route should be taken first.
If that fails, it's something the community cannot handle or the problem is urgent then please flag for ♦ moderator attention and use the free-text flag.
6: … is spam or offensive?
Flag as spam or offensive.
Note that even if a question is old and does not receive much attention, casting a close vote will put it into a review queue. Other users can work through the queue by casting their own votes or deciding to leave the question open. This means there is no need to flag old questions for moderator attention anymore.