Flea preventative for dogs?

I'm out of date on this - what's the best (least toxic) flea preventative for dogs? We used to use Advantage (which I guess is now Advantage II?) with good success since I've never had a problem with ticks on our suburban lot with most concrete/pool backyard. Or should I just get Frontline Plus from Costco? The only thing I worry about there is more chemicals that I may not need (for ticks) and the possibility that it may not work as well (resistance) because everyone uses it...

I also tend to only use a flea treatment when I notice fleas, rather than every month.