Either of those options are fine. You want your cold environment to stay cold. The hardware requirements are minimal for generating keys and signing transactions. Of the machines you listed above, I'd go with whichever machine you are most likely to keep offline and cold. Disabling WiFi and Bluetooth in the system BIOS, as well as a fresh OS install before key generation would be best. Also, remember to follow offline workflows for system, node, and software updates.
I use an old laptop and keep it tucked away until I need it.