I usually go to Advantage when the flea season starts (and it always worked good), but Costco had the cat Frontline and I tried that this time (I figured they were all pretty much the same).  Boy what a MISTAKE!!!!  My flea population EXPLODED on Frontline!!!  I had my 2 cats and 2 dogs on the Frontline, and they were all itching and scratching with fleas.  I waited for the month (literally picking at least 30 fleas off each of my dogs every night by hand to try and help), and then went back to my Advantage.  The day after applying Advantage, I found 1 flea on my dog (I have long hair cats, and I cannot see the actual fleas on them, but I can on my dogs)  and it was almost dead, it just fell off her (on Frontline, I went from having about 15 fleas fall off my dogs while bathing them before the application, to almost 100 while they were on it, so they had A LOT of fleas when I applied Advantage).  My cats are not scratching constantly anymore.  In 1 day, this product did what the people at Frontline told me would take up to 6 months for their product to do!!  Advantage SAVED my animals and house from being COMPLETELY infested with fleas (gross).  This stuff is amazing, and I will always use Advantage!!!