The easiest way would be to use a service like Scrubly, which can take multiple address books into it, merge all the duplicates, add social media info, and give you a clean contacts list that you can use. Second, you can export your contact lists from other services, choose the one you want to sync with, and import them there, clearing duplicates manually as you go and only leaving the one service on.
First, you can sync with the OS X Contacts app and look for duplicates manually, which is a pain.
