Which of the following provides the best support for a structure?

Deep foundations are designed to transfer a building's load deeper into the ground, reaching more stable soil or bedrock. This is particularly important for structures that are heavy or situated on weak or variable soil conditions, where shallow footings might not provide sufficient support. By extending into more stable material, deep foundations significantly enhance the overall stability and load-bearing capacity of the structure.

Shallow footings, while effective in many scenarios, may not adequately support larger or heavier buildings, especially in less stable soil conditions. Sloped surfaces do not provide any inherent support for vertical loads and are not suitable for building foundations. Piers can be used as a form of deep foundation, but they are typically employed as an additional support system rather than the main foundational method.

Therefore, deep foundations stand out as the most reliable choice for providing long-term structural support, especially in challenging conditions.