i like Frontline combo due to the fact that my cat went to a cattery and came back covered in fleas i previously was using a flea spray.
I used frontline combo and it worked miracles i also used the household spray bought from my vets.
I would also suggest you get your cat wormed if he has not been already just to be on the safe side as if he were to ingest a "bad" flea he could get worms.