Flea Treatments for Cats....Recommendations?

I have 2 cats. Neither care for the once-a-month flea drops but the older cat (3 yrs) will itch and bath himself frequently in the few days following his new monthly dose and then be back to normal.

The other cat (a girl) scratches for a week or better. Her fur on her back will still twitch at random for several days as well.

I switched brands for her benefit thinking maybe she was allergic to one. She did okay until about this 4th time or so....now back to scratching constantly. It is the kind in a purple tube you cut open (1 per cat) and a 3 month supply for 1 is about 9 bucks.

They have never had fleas in the house or on them that I've seen in the 3 years I've had cats in the home. I don't think the flea collars would work well, we had them growing up on cats and since they've not been accoustumed to collars I hate to start it now.

Can you honestly recommend a favorite brand for a sensitive skinned cat treatment? I will try the pet stores in the next week or so but I guess for the month of June they are already covered, just can't reuse the treatment on the girl cat again....Hope you can help me (and kitty!). She sends her thanks too.