martinibuster - 4:10 pm on Mar 8, 2013 (gmt 0)
I agree with the test and see. However, here are some considerations I use for my sites.
1. My assumption is that site (English language) visitors scan a page from left to right. I'm currently doing tests with left and right placement with large rectangles. Surprisingly, so far, middle of the page right placement is earning better than top of page left placement on a long article. That's just a preliminary result. Long term results may differ. I encourage you to create channels for left and right placements and further divide them by top, middle and bottom of the page to find the optimum placement.
2. Page organization can be conceptualized as on a grid, with content blocks organized in a left to right pattern. Content blocks are further divided as above the fold and below the fold. Do consider that when placing ads and testing them.
3. Center aligned. You can use CSS styled onto a div to place ad content smack in the middle of content, with words flowing around it. Don't forget the center placement. Yes, for that size ad unit it could be a negative user experience, but just want to point out it is an option.