Bitdefender or Malwarebytes (for Mac)?  Or both?

I would say malwarebytes, especially the paid for version - by the way ccleaner isnt antivirus or security software

Unless you go to dubious websites and download software from pirate sources, neither are necessary on any Unix-like OS.  

Id suggest going for Malwarebytes cause it can find and detect and quarantine what lot of anti viruses cant find. Also its good at protecting computers