Good topic – it completely depends on the demographic you are targetting but on the whole I would say that text links convert better than banners.
Banners are great to catch someone’s eye and create a brand but if you are getting players that click on a keyword (text link) within an article, the chances are the player is one who is reading up on a particular operator is one who will spend more money. That’s my opinion and is not always true though.
The best thing to do is have different tracking links/codes for each banner/text link and then monitor the conversion percentages 