I use a narrow skyscraper on the left, starting where the content in the article starts. No more than one adblock per page.
As the previous poster pointed out, you have to make some decisions about what "best" means. A big rectangle at the top of the page might be best for income, but not good for visitors, and thus not good for building up the reputation and inbound links of your site.
There are a bewildering number of possibilities, considering formats, placements, and colors, but if you are clear on your goals, you can zoom in on a few that best suit your site, and see which one or ones work best.