Many times you will see "Top ads" or "Top performing" banners when you visit an affiliate panel. Most Rival Casinos have that and there are a few other backends that will show the best performers.
Personally I prefer a banner that does not look like the Vegas Strip. Not a ton of flashing. In this day and age I think that the banners should be a compliment to you article... add color to a page and not distract from the well written ad you have. For me, text links out perform banners and I am sure that is the case for most all.
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"People who are unable to motivate themselves must be content with mediocrity." ~Andrew Carnegie~