Both Frontline and Comfortis are reliable flea control products. It is important to understand that neither of the mentioned products will repel fleas and with either the flea will have the opportunity to bite your dog before it dies and it is the flea bite that triggers an allergic reaction. It these products are used continuously it is possible to eliminate all the fleas in at least your indoor environment and thereby avoid exposure for your dog and also then the allergic reaction. There is evidence of developing resistance to fipronil the active ingredient in Frontline which has led many veterinarians to suggest Comfortis, but them tick control is sacrificed.
Frontline Tritak, a new collar called Seresto and Advantage products have repellant properties which then reduces the risk of flea bites and the resulting allergic trigger.