For a more generic answer, you should buy a USB 3.0 device because the new computer you buy will support USB 3.0. The 3.0 device will still be backwards compatible to the 2.0 ports on your old computer. When you copy from the old computer to the device, it will copy at 2.0 speed but when you copy to the new computer, it will transfer at 3.0 speed. However, don't go with a device that uses a USB C connector since the new computer might have but your old computer doesn't so it won't be able to connect to the old computer unless you buy an adapter.
USB devices are always backwards compatible so when buying a new USB device, always buy the latest version.