I now use 1 ad unit and 1 link unit per page. Either way, the highest paying ads shot, and the link units have added clicks to my total numbers.
One, because I've already got affiliate links and a banner, and I don't want the site to look so ad-heavy that users don't come back.
1 ad unit for me!
I had 2 or 3 on some sites but I cut them all down to 1. CTR decreased but eCPM remained around the same, perhaps a little less.
I'm pretty sure it's paying off. My sites don't look like spammy MFAs anymore! I'm sure the users appreciate it.
I am currently doing some testing to see what the results of 1 ad unit vs. 3 on one of my websites.
The results so far (around 20 days) is that one ad unit with only two ads (the one called banner) - generate the same revenue as before when i had 3 ad units with a total of 8 ads showing.
The next test i am going to run is to replace this ad unit with one with 4 ads vertically (medium or large rectangle) to see if this creates different results.
1 Link Unit 728x15
thinking about switching the leaderboard with a 468 banner
1 AdLink 160 x 90
Adlink provides 40-50% of earnings
One very niche site has 73% AdLink earnings.
My experimentation has shown that the more ad units the lower the EPC therefore eCPM.
I've gone to one leaderboard per page in the hotspot at the top. Used to have a footer banner on the bottom but CTR was horrible. Since removing the footer, earnings have gone up. I think using one ad and one link unit per page is where most sites will hit the sweet spot.
Most of my pages have one 300x250 and one 160x90 (4 links) Adlinks unit, 1,200 or so pages. Individually these pages don't perform especially well, but there are so many of them, and they get so much traffic (relative to my overall traffic numbers) that they provide most of my income. I'm testing a few of these pages with a third ad, just above the main content, a 234x60, so far the results are ok, but nothing to brag about. But none of my pages are in the "brag about" category anyhow, so the incremental growth is appreciated.
A fair number of pages maybe, maybe 100 or so, have a single 250x250 adblock. The performance of these pages runs from "why bother" to "very good", I haven't got a clue why, someday I'll spend the time to figure it out.
25 or so pages have a 120x600 regular adblock with a 120x90 Adlinks unit above it. These are the worst performing pages on the site, mostly because of the way they are used. It doesn't really matter to me because the ads are in the only spot (righthand column) that I was willing to give up for ads, so they do what they do, and that's good enough. At this point it's there or nowhere on these pages as far Adsense goes.
On most of the pages I have 2 units which has worked for me as the best.
I normally have 1 (or rarely 2) other ads (chitika, graphic banner) too.
2 google ads per page works for me, along with 2 or 3 CPM banners from FastClick, maybe Chitika (not doing very well) and on some pages AdLinks (they are very relevant and work well for me on certain pages).
My pages are ad-rich in keeping with my long-standing concept that content (or in newspaper parlance, copy) is only there to take up space in proximity to the ads.
I write solid content - have for more than 20 years - but I am a realist. It's worthless unless somebody pays for it, in this case, advertisers.
The more the merrier. I write some lengthy articles at times - 2000 words or more, and I now break them into 2-5 pages. Works for me.
My simple-minded formula: more pages + more traffic + more ads = more revenue.
One ad - much better ctr, and smart pricing seems to prefer a stable, healty ctr over the longer term. Therefore for me, one ad block earns me more than several on the page, AND it doesn't look like a spammy click trap MFA site either. Which I have to concur with the earleir potser, visitors appreciate.
1 ad unit, sometimes with an ad link unit too.
4 ad units work best for my web layout and have created the highest CTR. It really depends on how you decide to weave the ads into your site.