What non-cloud backup?
Currently use thumb drive and running out of room.
More thumb drives?
USB hard drive?
Solid state usb drive?
I have three hard drives for backup in my Mac Pro. One is a complete, bootable clone, and the other two are data only. I use an external enclosure with a (USB) hard drive for my PC backup.
I think a USB hard drive is fine for backup, as it doesn't need to be super fast, just reliable.
I use a thumb drive to transfer data from one PC to another, but I can't imagine using one (or many) for backup. That would be a pain.