I think you're safe with either. I've known people who've used both products with success. Just try one, and if it doesn't work, get the other one. You might want to talk to the vet about this just for reassurance. :)
Hi Jeff,
Well, I've always used Frontline and my vet, who I totally trust, swears by it. I work at a shelter and with a rescue team and we always give it to the cats we work with.
I think you're safe with Frontline.