Generally, the capacity of USB flash drives is limited, such as 8G, 16G, etc. If you have less information, such as documents, you can give priority to using USB flash drives.
If you have a large amount of data, including not only documents, but also common software and system backups, it is recommended to use a hard disk. The current hard disk price is about one yuan /G, which is not very expensive, and the transmission speed will be faster if the capacity is large.
No matter which one you choose, you should take good care of the U disk/hard disk, just like an advertisement said: the hard disk is valuable and the data is priceless!