I think that the best way to find out is to track your ads. I use trck.me tracker and I never place an ad without adding a tracked link. It takes a bit of time to see which ads are being clicked on and to determine where your traffic is coming from for each ad. Then it's only a matter of using the ads where you get the best results or fixing the ads that get fewer results. Sometimes you will find that you are getting results from the least expected places.
