Meds safe for small dog?

Good evening!

I recently adopted a toy poodle. She is currently 4 months old (DOB 7/13/12). I've had poodles all my life, or I should say my parents have had them - this is the first one that is mine! My vet gave us samples of Heartguard/Frontline. My parents have always used Revolution, but their poodles are slightly bigger (10-12 pounds). Lily is projected to be only 6-7 pounds, and I'm worried about the effects of the medication on her when she is so small. I asked my vet about one option versus another, and she said it was all a matter of preference and my choice what to get.

So this would be my question: is there an option out there for heartworm/fleas et al, that is tailored/less toxic for the little dogs? (For example, I see one that has a 1-10 pound dosage, but another that is a 1-22 pound dosage. That's a huge difference metabolically if the drug effect is linear. (Sorry...scientist by training. I over think these things sometimes.)

Thank you very much for any insight you may have. It's going to be fun finally having a poodle of my own after all these years, even if she is smaller than I'm used to having.

Robin