I prefer advantage, mostly because Etain who is allergic to everything under the sun had a reaction to frontline. She seemed to tolerate advantage ok, and it worked, in one month no more fleas, we didn't even need a second application.
If you have a really stubborn flea problem and advantage just isn't doing it, you might try frontline, I heard that it kills fleas in their larval form as well as adults ... however, I have heard other places that larval fleas are immune to pretty much anything and that you just have to keep killing the adult fleas until there aren't any left to lay eggs. I'm no expert on the subject, this is just what I've heard through the grapevine ...