Transferring data between iMACs

You basically have three choices to connect these two Macs:

1. Connect both computers to the same local Wi-Fi or Ethernet network.
2. Or connect both computers directly using a Thunderbolt or Ethernet cable.
3. Or connect your new Mac to a Time Capsule or external drive that has a Time Machine backup of your old Mac.

To directly answer your question, you could use either an Ethernet or Thunderbolt cable to connect them together.

Hello, ellevi.

Per this Apple support document, a wi-fi connection is all you need. But... wi-fi can be flaky.

Move your content to a new Mac - Apple Support:

https://support.apple.com/en-us/HT204350

If your new iMac is of the flavor that has an Ethernet port on the power block, an Ethernet cable is the best way to transfer data between the two iMacs.

Please follow the steps in Setup Assistant and Migration Assistant to learn the fastest, easiest and most reliable method.

With all due respect, Ethernet is slower than a USB cable connection is. I would recommend USB. Do not use Wi-Fi as it is way too slow for these very large transfers and will often fail.