I spoke to my vet recently about flea and tick medications. Her feeling is that we should use the least amount of chemicals on our dogs that we can, which I agree with 100%.
Every area is different, but she found this works for our area (southern ontario):
Assuming there are no fleas already in your house, nothing from November/December to the end of March since fleas can't typically survive the cold, unless they're living in your house.
From April to June, Frontline Plus for flea and tick control. The ticks here don't seem to bite too much after June, only in the cool, damp weather.
From June to Septmember, Advantage for fleas. She feels that Advantage is less harsh and should therefore be used in place of Frontline Plus if ticks aren't an issue.
From September to November, Frontline Plus if ticks become a problem. If not, Advantage for fleas. I haven't found a tick on Sadie since May/June. Fleas have been a big problem, which Advantage has helped tremendously.
There is one problem here though: Frontline and Frontline Plus are not available in Canada. Not sure yet how I'm going to get it for next year, I'll either order it online or have to make a trip over the border to get it. I'm told that Target sells it now.