fumanchu - 6:14 am on Nov 14, 2013 (gmt 0)
Depends on the day, oddly enough. I've seen days where the bottom one kicks ass and then vice versa. So I leave them both there and it works out fine. There's no way to predict which will do better on a consistent basis.
Just put one before the content at the top of the article column, and one after it right after the content ends. If you need to then make your article column wide enough to fit the 728x90 right over the title of the article. Don't put it way at the top of your blog, it should appear right in the article column itself.