After switching from cheap-o junk to Advantage in November 2010, I can tell you that there's virtually no reason I'd use anything else. I think the only reason I'd  use something else would be to alternate with Frontline, since I've read that alternating the pesticides helps reduce the chance of the fleas becoming resistant. Haven't done that yet but Advantage/Advantage II have worked wonderfully. After getting a nasty flea infestation under conrol in Nov/Dec 2010, I haven't seen any fleas, nor any signs like out-of-the-ordinary scratching. I even stretch the applications from every month to every 6 weeks to save money. I saw some alarming side effects from the cheap drops but haven't seen any issues in the cats with this stuff. It has really paid for us to spend more. As much as I'd rather use something natural (totally useless here), we love this stuff!