Final answer:
The Mini-ITX is the smallest form factor among the options given, making it the best choice for saving space in an office environment.
Step-by-step explanation:
When comparing case sizes to reduce a computer's footprint, Mini-ITX is the smallest form factor mentioned among the options given. A full tower and mid tower are larger and suited for users who require extensive expansion capabilities. The Micro-ATX is smaller than full and mid towers but is still larger than the Mini-ITX. The Mini-ITX is designed for compact builds and is ideal for saving space while still providing enough room for basic computer components.