just let me start by saying, Apple has gone down the toilet since Steve Jobs passed on. its just the truth. anyway with that spray of frustration out of the way....
the best way is to do a back-up on a backup drive of the source computer, and use this backup drive for the migration source via USB or thunderbolt (if your backup drive is a thunderbolt one). it works way way way eway way quicker
do not try via Wifi. we will all be dead waiting. no disrespect to the dead or Steve Jobs.
check out other forums. they all confirm this as fastest way