Fiber when ever possible. It usually has higher bandwidth, is less affected by noise, magnetism, and other interference. Also it has less drop over distance vs wire.
As a word of caution, most cables that say they are Cat8 usually do not test out that way. It's very important that they use cat8 ends, and install them correctly.
@mswale Some decent streamers are designed to successfully decouple/isolate the above mentioned making the upstream ethernet/fiber infrastructure tweaks a bit pointless. Some don't and benefit from the same.