This is a list that I have discussed many times with friends, however I never found these on a single place so here you go ...
Differences between iframe tag and script tag:
- Script tag does not change the “referrer” property of your ad-tag: If your ad-tag is served from inside an iframe, the ad-network that serves the ad will see a referrer property different that your page url/domain. On the other hand if you use a script tag, then the referrer url remains the same as your page url and therefore your domain name. Some ad-networks that require that the ad being served from the same domain that they were created for, will therefore not work with iframe tags (therefore they will not serve ads). Most ad-networks however allow setting of a “site-alias” that allows you to set a different domain from which the ad may be served. Read more about the referrer property here.
- Script tag works better for ad-networks that do contextual analysis of the content of the page: if you use iframe tags, ad-networks will not be able to look outside of the iframe therefore they will not be able to do on-the-fly contextual analysis of the contents of the page, therefore they may serve irrelevant ads. Read more about contextual analysis here.
- Iframe tags are easier for inclusion inside a web-page, since you can save an ad-tag in a file, and load it as an iframe into your web page. This will also allow parallel load of the ad-tag iframe. For example if your web-page is: