The artificial sweetener that has the highest sweetness value in comparison to cane sugar is:

The relative sweetness of an artificial sweetener is expressed as a numerical factor that tells us how many times sweeter it tastes than ordinary cane sugar (sucrose). The bigger this factor, the sweeter the substance per unit mass.

We list the well-established sweetness values for the four sweeteners mentioned:

Sucralose     $$\approx 600$$ times sweeter than sucrose,

Aspartame    $$\approx 100 \text{ to } 200$$ times sweeter than sucrose,

Saccharin     $$\approx 550$$ times sweeter than sucrose,

Alitame       $$\approx 2000$$ times sweeter than sucrose.

Now we compare the numerical factors one by one. We observe that

$$100 \lt 550 \lt 600 \lt 2000.$$

Because $$2000$$ is the largest number in this ordered list, the sweetener having this value clearly possesses the highest relative sweetness. The substance associated with $$2000$$ is Alitame.

Hence, the correct answer is Option D.