I've always used Advantage on my cats - it's what the vet gives me when they need it, and after a HORRIBLE* experience while visiting a flea-filled house in Maine, it works for me.
*I first used a "natural" flea collar on them - a cotton collar that you applied a natural flea repellant oil to, which did not work at all. I ignorantly applied some of the oil to my cat's feet, which he immediately started licking off, then FREAKED OUT because it tasted so bad. The whole thing ended with me in tears, thinking I had poisoned my cat, on the way to the local vet. They gave me Advantage there, too. Needless to say, that was the cats last visit to Maine.