fastest connection method for migration process?

What is the fastest physical connection method for a mac-to-mac migration process?

I want to use migration assistant to move all data from an old iMac with ElCap to a new iMac with HiSierra.

I'm assuming wi-fi is never the fastest method, but not sure what's best connection of other choices (i.e. ethernet, thunderbolt, usb, etc... assume firewire is out since its gone on new iMac).

Thx for advice