Dear,
Thank you for this question, this is very important question that all publisher should know!
Text links ver Banner Ads
Text links are proven to be far better result oriented then the graphical links. Since you can put the text link inline with your text so that user pays more attantion toward it.
You can put only a few banners on your page but you can put several text links on a single page!! and best of all, text link does not look like an ad so that user clickthrough ratio is more then banner ads.
Furthermore, You can not change the banner ad, but you can put your own text just before and/or after the text link to make it more personal. for example, your text link says "World's online marketplace", you can add some text and make it like.. "I always use this online marketplace because of it's low prices and better quality, no wonder it is called World's online marketplace"
This way you can make it even more attractive without changing the original text!
Hope this answered your query.
Hashim Taylor
http://www.HashimTaylor.com