I previously used Advantage to take care of my cat's flea problem, and it worked immediately - but my cat absolutely hated the smell which lingered on her body.  She would howl and run off when she saw me approaching with the Advantage vial, and I hate being the villain once a month. So now I've switched to Program.  It's kind of a pain mashing the tablet and mixing it up into wet catfood.  Also, it takes a couple of days to take effect.  But - it does work well, and my cat is very happy. I will definitely buy Program tabs again.