For a while, a lot of the gurus were saying to only use one AdSense block at the top of your page and it would raise your eCOM because your overall click rate would be higher so Google would raise the amount you were paid per click or something like that. This based on the fact that ads at the bottom of the page have a lower overall click-thru rate than ads above the fold, which lowered your average overall so advertisers perceived your clicks to be less valuable.

Lately, I've been seeing more and more people saying to go back to the maximum amount of allowed ads.

Which theory do you support?

That is an interesting theory for having just one adsense block. I had never heard of it, and on most of my pages I have three blocks (if the page is big enough to have that many without looking cluttered by ads). The pages that are small and don't have any below-the-fold space, I just have one block usually.

I usually have 2 or 3 blocks on a page. I've never heard that theory but its an interesting one.

i've done tons of testing, and i've always made the most money with 1 creative per page.

I did a little testing and found that it worked out that I made only just a little bit more with 3 ads compared to 1.

Might be coincidence but I've earned more with less. Go figure

Heres why you make more with less. The top 3 ads that show up always pay the highest. Position 1-3 no matter what pays the highest, and i've tested tons of strategies with arbitrage. My page with one large ad unit was paying me more then double then if I had 2 units because the drop to 4-6 was high enough, plus people weren't clicking as much seeing more ads. It really depends on the situation, and if you have something where the ads 1-9 are all worth a lot then you are better off to have more ads but spread out.

I use one 336x280 block per page.

I put all three unit ads on each page.

I tend to not go for the either extreme 1 or 3; hence I stick to 2 big square blocks.