Superior means anything which is better in quality and merit than other thing.
In this sentence superior is the most suitable option because of the preposition “TO” used in the sentence .
The sentence needs any comparative adjective in which preposition TO is used with it. While better is the most commonly used comparative but it needs preposition than and hence it cannot be used here.
Hence superior is most suitable answer to this question.
The others don't make any sense and you could do the process of elimination so you would eliminate lesser and few so then your left with the words less and fewer but in this case fewer makes the most sense.
