Logistically — for Google — option A is the best option.
Option C is fine too. Like Linda said, the same team needs to deal with this particular case. The contact forms take you to our Google Places support team, who routes your dupe report to the team who will work to fix it. So it's an extra step for everyone involved to getting these things cleaned up. But if a personal response makes you feel better about it, then go for it.
Duplicates take several weeks to clean up, and often even longer than that depending on how messy the situation is. We see *all* the "Report a problem" reports, whether you get an e-mail confirmation or not.