Best spots for increasing CTR

I know testing is the way to go, but from your experience....

[Automotive site]

I know it can vary by type of site, but there must surely be a trend.

I have been debating with myself whether to move the 728 banner just under the site header to bottom of the article (or 336 by 280).

I have always suspected the very spot will probably be one embedded in the content somewhere above fold.

[nomis5]

It does vary enormously by site. For my sites it was 336x280 but now 300x250 seems better.

Position always has been above fold. Slightly right or left of center seems to work best.

One problem though in making any analysis of best size / position is that some advertisers only offer ads in a limited number of sizes. If one of those advertisers is paying good money it can temporarily distort the results.

[jbayabas]

For my sites, it used to be 728 banner but now the big box 300x250 middle of content is much better hands down.

However, CTR may also depend on your niche and keywords.