The best time to move you data is on first run of your new Mac. Instead of entering a new Account, you tell it to use your old one, and connect up either a time machine backup or the original computer.
Apple suggests you use Wi-Fi not because it is especially good, but because it works and is easy, but it is generally not at all fast. Third party sites suggest that it takes so long, sometimes it quits in the middle. There was a new twist I had not seen before -- it your old Mac was running 10.11 El Capitan or later, bring your computers close together, and rather than copying through your Router, it may copy Mac-to-Mac.
You can also use Thunderbolt cable Mac-to-Mac, using this guide to assign an IP address. It should be very fast:
Use IP over Thunderbolt to connect Mac computers - Apple Support
Or Target disk Mode:
Transfer files between two Mac computers using target disk mode - Apple Support
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