which method for OF for Mac is fastest?
 

I use OF on my two macs, where synchronization is made very often.

Which sync method should I use IF speed is my concern?

The Bonjour sync will be the fastest, unless they have a common disk they both mount, in which case setting up the disk syncing might be competitive. Usually the big bottleneck will be uplink speed, so a solution that stays on your local network will beat one where traffic has to leave your network and go to Apple or Omni or other 3rd party server.