OK. Ad Optimization is an essential part in Earnings. BUT there are many questions to be answered:
1. Which is better: ads above the fold or within the content?
2. Which is better: ads on the left, right, or center?
3. Which is better: ads that blend in with the site or ads that constrast the site?

For one and two the google heatmap shows what places on the page recieve the highest CTR. But in practice it will be different for every site, So it's best to set up channels to monitor each ad blocks performance.

For three i would say the adverts should be similar enough to your sites colour scheme so it doesn't look like you have adverts on the page, But different enough to catch peoples eye. I tend to use the same colours in my ads as i do on the rest of the page, But make the colours in the ads a shade or two lighter or darker.

Go and google "adsense heatmaps". It gives you all the info u need.

The Google Heat Map is a good place to start to see where ads might be most effective, but as stOx mentioned it can vary for different sites.

Ultimately you'd want to set channels to measure which ads perform best for your particular site.

With the blend or contrast I'm believe pretty strongly that blending is better, but I've seen people report having better success with ads that stand out.

To really find out though you need to test different ads in different places on your site and see which works best for you.

Thanks, guys, for the input. The reason I asked is because one site says this, another says that, so I needed a definite answer. I believe the only option to finding these answers is to EXPERIMENT.

I think some of the reason you'll get different advice is that success can vary some with each individual site. That's why the best advice is really to experiment a little with different ads in different places and measure those results. Learn to set up channels so you can see which ads are utlimately bringing in more money. Get rid of the underperforming ads and use more of the ones that work well.

AdSense will most likely pay the best by tweaking things based on the testing and measuring you do.