does migration assistant work with ethernet?

Yes - ethernet will work -- like network drive ...etc.

Avoid wireless connection at all cost.

Many times Ethernet works however if you want the most reliable method of using MA, please follow the steps in Setup Assistant and Migration Assistant. If you do not have a Time Machine backup (you can also use a bootable clone backup) then create one! You only need an External Hard Disk and Time Machine is built into Mac OS. You can use the External Hard Disk for the new Mac as it will need a backup plan. The External Hard Disk I (and many other experienced users) prefer is the OWC Mercury Elite Pro due to it's high reliability, easy of upgrading, reasonable pricing and vendor support.

From experience, the best connection is to use a USB cable connecting the two computers. It is simply too much data being transferred for a Wi-Fi transfer. It's too slow. Corruption often occurs.