Generally I don't use anything, but if I do it's usually Frontline. I used Certifect once or twice last year because I had some free doses, but I think that stuff is way too harsh for my suburban dogs that are in no danger of being mauled by ticks.
I have heard good things about Sentry Natural Defense but you always have to take into account how much of an issue fleas/ticks are in your area. I don't think fleas are really a huge problem here - at least, I have never known anyone to have a pet with fleas - so when people say their dog didn't get fleas/ticks on this product, well it really could have nothing to do with the product and just be that they weren't exposed to them
This year I don't plan on using anything!
ETA Fran how much of everything do you use in your little spray? I might want to have a little something like that on hand, mostly for Happy because it wouldn't be as easy to spot a tick on her like it is with Juno.