For me it's the Large rectangle ad, of course it all depends on your CTR % and traffic and rank position. But for me it's doing very well. Share your thoughts!
Regular sized ad 728x90. Also: http://support.google.com/adsense/bin/answer.py?hl=en&answer=17955&ctx=as2&rd=3
Banner ads have always performed well for me....I'm using a banner ad just beside my post title and it is working quite well there...I used to use another one i.e. wide skyscraper of 160*600....It also performed quite well for me.....I would suggest you to use one banner ad around your post title and a rectangle or skyscraper in your sidebar. This combination really worked for me...
When you create an ad in google adsense you have this option when you select the ad you want its down the bottom of the list.
I have an ad right after the first paragraph on my site. It is a square ad link and I make it so that it is only text ads. This tends to give me the most CPC as well as the more CTR. Good Luck Man
The best ad placement for me has been the 300x250 left aligned floating header. I use the FREE ad injection wp plugin for this and it places my ad very well next to the 1st paragraph. Try it out you will be amazed with the results, for me its worked till today. Hope this helps someone make a decision on an ad placement to try.