By the time you start seeing fleas, it is late in the game and will take anywhere from a few months to as long as 6 months to get the problem resolved. Each flea lays 30 or so eggs per day. These eggs fall off the pets and end up in the environment... couches, carpets, bedding, etc. Even if you get rid of the fleas on the pets, 95% of the flea population remains in the environment.
The flea eggs hatch to become larvae, which are tiny little worms, then these form a cocoon stage called pupa. The eggs and the larva can be eliminated by spraying the house but the pupa can't. Nothing kills the pupa. The pupa hatch to become adults so when this happens, if there are flea products on the pets, the adult fleas will die.
So to your question...there are several good options. The most important thing is consistently applying a high quality topical to the pets every month, year round. I would use Frontline as it is very safe for cats and dogs. Don't use cheap brands that are less safe and less effective. Dog products are generally not safe on cats. In the ER, we see several cats per month that come in seizuring because dog products were applied to cats.
Spray the house with Knockout Spray. Follow the instructions closely: click here
Spray the yard with an area treatment - focus on shaded areas. Immature fleas don't survive direct sunlight: click here