I have tried almost every combination of placement, size and colors and have found that the set out of the site and the content on the pages makes more difference to just placement and color. Is there a perfect combination ?.
This varies from website to website because everyone has different layouts. Generally, adsense placement should blend in w/ your site's color scheme. What is your site's url?
Like 8everything said, it all depends on your website. There is no "perfect combination" that works with every site, but generally, the default adsense style works quite well if you have a white background.
Agree with you you cannot just try any color and placement, the important thing is that it should go well with your website or else the placement and color is of no use
blending is very important, makes your site more attractive and professional...and adds more interest to it...