The governing principle is that throttle response depends on how quickly heat can be turned into pressure on the piston; the more direct the combustion, the faster the engine reacts.

In an internal combustion (IC) engine the fuel burns inside the cylinder and the resulting gas pressure acts straight onto the piston, so power appears almost the instant fuel is burned.

Because combustion is directly tied to the fuel and air let in, an IC engine can change its speed and load rapidly, giving brisk acceleration.

An external combustion engine burns fuel outside the working cylinder to heat a separate working fluid, and that heat transfer is comparatively slow to build and change.

A steam engine must first raise steam in a boiler, so it cannot respond quickly to a demand for more speed.

A Stirling engine relies on heating and cooling a sealed gas through the cylinder walls, which likewise responds sluggishly to rapid speed changes.

For a vehicle that must change speed often and accelerate quickly, the fast, directly-controlled internal combustion engine is the suitable choice.

Hence, the answer is Internal combustion engine.