I’ve been banging my head against the wall with the same problem for years. Started with Act! in the early 90's and eventually migrated to Outlook, used Xobni for a while until that wasn’t supported any longer and gave DejaVu a try. Switched to a Mac last year and now have contacts in the Apple program. I have multiple google accounts, linkedin, Facebook, twitter, etc. I have a huge problem with duplicates. Recently have tried full contact, but they don’t have an android version yet and don’t think it works with the apple contacts. Will give full contact more of a shot as does come highly recommended.