336x280 is by far the best performing ad unit for me. And instead of below your content, you might want to consider adding one unit inside your content, above the fold. If done well, your ad will not be obtrusive.

We use to do very well with the 336x280. However since they changed the clickable area of the ads, we switched over to ads with a bigger font (hence a bigger clickable area).

We now use the 160x600 as our top earner. It has very good size fonts/ads that are easy to read. Does very well for us when embedded on the left side of our content.

Beyond that we supplement with the 200x90 link unit at the bottom of our content. It then comes in second as far as earnings go, but seems to do better than a regular link block, since it shows some different keywords/ads. Mixes it up a bit for our users.

336x280 is by far the best performing ad unit for me. And instead of below your content, you might want to consider adding one unit inside your content, above the fold. If done well, your ad will not be obtrusive.

Most of my content fits into 600x600, so no place for 336x280 in the content

Thanks for sharing Your experience

Since some hours in test

1st version of new layout

Below the content, in the color of the naviagation

768x15 AdLink
768x90 Banner
Subscribe to news Letter

New version just in test

+-------+------+
¦336x280¦200x90¦
¦#*$!#*$!x¦Subscribe

It's now to early to say it's definitive better,
because I test only at 15% of my earning inventar,
but for the first 6 hours, 2 newsletter subsciptions
and several clicks on the new ads below the content

I think after watching some more hours,
I will change the 85% rest of my inventar