@User1974 In my personal opinion topical liquids that you apply to the neck work best because they are easiest to administer. Many cats refuse to swallow pills or other medicine and washing your cat with anti flea shampoo is a nightmare for both you and the cat
@Elmy And keep it up plus clean/treat your home. You don’t want a flea-free cat get reinfected on a cat bed (or couch, bed, rug,…) where the eggs remained.