The planet that moves the fastest in its orbit around the Sun is Mercury.

Here are the average orbital speeds of the planets in our solar system, listed from fastest to slowest:

1. Mercury: 47.4 km/s

2. Venus: 35 km/s

3. Earth: 29.8 km/s

4. Mars: 24.1 km/s

5. Jupiter: 13.1 km/s

6. Saturn: 9.7 km/s

7. Uranus: 6.8 km/s

8. Neptune: 5.4 km/s

Therefore, Mercury has the fastest orbital speed among the planets mentioned in the question (Mercury, Jupiter, Mars, and Saturn).