For dogs, use any of the prescription oral flea medications that have been coming to market recently: Comfortis, Trifexis, NexGuard, Simparica, Credelio, and Bravecto.
For cats, use prescription Revolution Plus or Bravecto for Cats. Although applied topically, this is a systemic medication that absorbs into the body instead of sitting on the skin.
Topical flea products (except Bravecto and Revolution) are EPA-regulated pesticides. They are on your pet’s skin for up to a month, and you are exposing your family and your pets to these pesticides continually. They also are not working as well as they used to. Many topical products for dogs contain ingredients that are toxic to cats in your household. Some topicals are basically flea spray in a drop - completely ineffective.
Flea collars aren’t so great. We have long seen many allergic reactions to the plastics in the collars. They are also exposing your family and pets to pesticides continually.
The oral products your veterinarian recommends really are safer and more effective. There is no need to regularly change which of these oral products you are using. Yes, there are websites dedicated to the supposed dangers of these products. If they really were that dangerous, their competitors would make sure every veterinarian sees the evidence.