If both sites are hosted locally behind the F5, you don't care about having multiple FQDN's pointed to a single Virtual Server, and you have a Multi-SAN SSL Certificate on the Virtual Server then I would go with Option C and use an iRule to split the traffic to separate pools based on the incoming HTTP::host value.
It is a cleaner solution with less construction and tear down, and it would be easy to redirect the traffic to your main site if your business should ever decide to dispose of it.
This is just my opinion though based on the information you provided.
Good luck with whatever option you choose.