Can I use an Ethernet cable to connect my old Mac to Mac new Mac using Migration Assistant. Or should I use Wi-Fi?

It should work, as ethernet adapters are pretty standard devices that should have built-in device drivers ready. I don't believe it really matters as it just needs a network connection, which can be a combination or Wi-Fi and wired ethernet. For example, I've got a networked printer/scanner and its only network connection is wired ethernet (no built-in Wi-Fi if you can believe it). But I access it with Wi-Fi on the same network, and the computers communicate with the printer just fine even though they're connected to the network wirelessly.

Gary645 Said:

"Can I use an Ethernet cable to connect my old Mac to Mac new Mac using Migration Assistant. Or should I use Wi-Fi?"

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Using a Crossover Ethernet Cable:

Not certain, but for Ethernet, you may need to use a crossover cable (typically colored yellow, by standards).

You don’t need to use a crossover cable. The macs will do the link adjustment automatically. Straight through cable is all that’s needed. If using Wi-do get as close to the router as comfortably possible, ie: be in the same room.

Antonio Rocco wrote:

You don’t need to use a crossover cable. The macs will do the link adjustment automatically. Straight through cable is all that’s needed. If using Wi-do get as close to the router as comfortably possible, ie: be in the same room.

It's not needed if they're native Mac ethernet ports. I did it for a late-2007 (Santa Rosa) MacBook to a mid-2012 (Ivy Bridge Unibody) MacBook Pro. It was pretty painless although it was using 100 Base-T from the slower port. Not sure how it would work if one is using an ethernet to USB adapter though.

However, I'm thinking that using a wired router makes it easier, in addition to being able to go wired to Wi-Fi.

Once you can connect each computer to the Internet without re-cabling, you have established a pathway that can be used for this Migration. A mix of Wi-Fi and Ethernet connections can be used, but most Wi-Fi connections are slower.

The most trouble-free way to use Ethernet cabling for this migration is to connect BOTH devices to your Router with Ethernet cables, even if you have to carry one or both over next to your Router.

The connection through your Router will be a local connection (through the Switch portion of the Router) not actually using the Internet-connected portion of your Router. But setup is much easier when the Router sits in the middle and supervises.

The easiest and most likely fastest would be to use your external backup drive - plug it into the new device and follow instructions.