I wonder what the difference between recommended ads and other ads are? https://support.google.com/adsense/answer/185666?hl=en I would love to have the medium rectangle (300x250) ad on my side column but the side column would be to big for my site so I have to go with the square (250x250) ad which is not under the recommended ads. How will using the 250x250 square ad affect me? is it a bad idea using the 250x250 compared to the 300x250, etc?
recommended ads are just the most popular, and make the most revenue... but its all down to the layout of your site to choose whichever fits best, and gets the most attention