I think banners are only useful if creative. For instance the first time I say sunpoker.com new SICK banners I had to click on them to see wtf was that about
Perfect example is Donkeylotto. We have had over 300 clients post their banners on our site and we know which ones work and which don't. I have seen more advertisers make money off non prime positions than those who buy the prime position banners....due to one reason. Their banners caught our visitors eyes and intrigued them to click. Its sales 101. IMO be creative and differentiate yourself in everything you do and it won't matter what you choose because it will work.