It really depends on your needs, as mentioned above, USBs can only handle quite a limited amount of files, while externals hard drives can store massive amounts of stuff. If you only need it to store a lot of word or excel files, then you'll be fine with a USB. But if you want to store or backup things like movies, TV shows, music, or other files with big sizes, then you're probably better off going for an HDD. I got a 1TB one for around $70, and I probably will not be filling that up for the next few years. So don't overspend and get something you don't need, just consider what your requirements are and go from there.