Step 1: Understand the question.
We must pick the storage device that holds the most data among a floppy disk, CD, DVD, and hard disk.
Step 2: Recall the floppy disk size.
A floppy disk is very old and tiny in space. It holds only about $1.44$ MB, which is less than one photo today.
Step 3: Recall the CD size.
A CD holds about $700$ MB. That is far more than a floppy but still small for modern needs.
Step 4: Recall the DVD size.
A DVD holds about $4.7$ GB, which is bigger than a CD because it packs data more tightly.
Step 5: Recall the hard disk size.
A hard disk holds from hundreds of GB up to several TB. Note that $1$ TB equals $1000$ GB, so a hard disk dwarfs the others.
Step 6: Compare and conclude.
Putting them in order, floppy then CD then DVD then hard disk, the hard disk clearly wins. So the answer is option 3.
\[ \boxed{\text{Hard Disk}} \]