Is Wi-Fi or a wired connection better for big cloud transfers and backups?

A wired connection is usually steadier, which matters more than raw speed for long uploads. In practice, your internet plan's upload speed and the provider's own limits set the pace, so Wi-Fi is fine for everyday transfers if the signal is good.

For a large first upload or backup:

• Use a wired connection or sit close to the router if you can.
• Keep the Mac plugged in and awake.
• Let it run in the background. If it's interrupted, running the transfer again skips files that already finished, so only the file that was mid-upload starts over — which is why a steady connection matters most for very large single files.

If uploads are slow to one particular service, that service may be limiting them. See are uploads resumable? and why Google Drive uploads are slower.