I want to try something different this summer. I've been buying different flea and then heartworm prevention products. The vet said that you need to rotate because around here with fleas being so bad they get immune to some stuff. I tried Frontline,Advantix2,and some natural stuff. All were O.K but I still seen fleas even with treating my yard. I've heard Revolution and Trifexis both were really good. If you had to pick which would you use?