Upgrading your storage
Running out of space to store all your home videos and photos? Do you partake in video editing and like to play in Photoshop? Has your computer been running slower than usual? Then look into getting a new hard drive.
External
External hard drives have become very popular in the last few years due to their ease of use and portability. External hard drives are good for long term storage and backing up your current hard drive in case of a failure. They are not suited however for running programs due to their lower internal and connection speeds. For an equivalent storage space, external hard drives are usually pricier than an internal drives.
USB
USB Sticks are better suited for short term storage such as transferring files from your home computer to work. They are also helpful for sharing files with your friends, especially larger files that are cumbersome to handle over the internet. Their small size makes them portable, easy to use and, unfortunately, lose.
If all you need is to store files long term or transfer files to school or work then either of these options would work fine for you. When looking at these options make sure it is compatible with your computer setup and if at all possible look for the USB 3.0 standard as this will make file transfer measurably faster
Solid State Drive (SSD)?
The difference between a SSD and a more traditional hard drive is that a hard drive uses spinning magnetic plates and a needle that moves back and forth quickly to read and write data on the disk. With a SSD the data is stored on flash memory chips such as a USB stick so there are no moving parts. This results in faster data transfer rates in most situations. The downside of using a SSD is price: a 128Gb SSD can be more expensive than a 1TB HDD.