Most likely fiber. Around here the ADSL provider (CenturyLink) was the first to start deploying fiber to compete with cable able to do 1gb (which is, of course, highly variable and full of asterisks because coax, quality to neighbors modems to support a stronger mesh, possible MoCA interference, etc.)
More recently they rebranded fiber as a different company… Probably to get rid of the DSL name stigma.
If you want to start the most effective, upgrade your router or primary switch to 2.5G or 10G. Then at least there is a low likelihood of a bottleneck when your devices are communicating internally with each other and youll have overhead downstream. Then, if you have multiple switches, prioritize the highest bandwitch between them over upgrading your devices beyond 1gb nic’s.
I use an opnsense router with 2.5g nic’s, and then I have a 2.5g switch and a 1gb switch than are connected via a 10gb fiber link. (This is all enterprise ubiquity level stuff). But all my downstream devices and switches are 1gb snd I have no plans to upgrade intentionally. Internally, I won’t see bottlenecks often since communication between the switches and modems is enough to support multiple devices spamming 1gb/s file transfers simultaneously (not that itll happen often lol)
So my WiFi access points, primary NAS, and my most used PC are all on 2.5gb connections since they could benefit. But everything else is on 1gb since the switch has way more ports and was way cheaper.
I’m not against buying 10g switches for future proofing, but they’re still too costly for my needs, and its unlikely I’ll wish I had 10g any time soon esp when it comes to internet. Even if I upgrade beyond 1gb fiber service, it’d be so thay multiple devices can fully saturate a 1gb NIC at the same time, not so one computer can speed test 3gb+.
Thay said, what I have is overkill, but i enjoy some homelab tinkering.