I guess it really depends. In adsense campaigns and results differ from one another. I suggest that you do it trial and error. But of course MINIMIZE the errors. Just go look for the strategy that'll fit you.
I find that 1 ad at the top of all of my sites is the most effective, especially ctr wise, people don't like to see loads of ads when they click a page. As for getting more $$ for less ads, I have never noticed any significant change.