The HTML versions can be printed directly from the browser. Advantages of this option are that (1) it is a simple "click and done" way to create a catalog, and (2) pictures of your auction items can automatically appear along with the descriptions. The disadvantage of HTML is that the pages cannot be edited or customized.
The RTF versions are Microsoft Word-compatible files that can be opened and edited in Word or any application that can import RTF. So you are free to add whatever design flourishes you wish.
More advanced users may opt to use one of the Microsoft Word Merge Templates we offer. Used in conjunction with the Paper Catalog Export report (available in Reports > Data Exchange Reports), you can generate highly customized printed materials using Word.
With any of theses options, you can, of course, create your own additional pages (cover page, etc.) and incorporate those when you assemble your final version for the printer.