Compare against your closest competitors > features, benefits, unique selling points, warranties, guarantees, return policy, shipping rates and methods... get specific, and uses everything and anything that provides a competitive edge.
If possible (and not joking) link to their products and show your superior integrity. There are many things you can do to avoid giving directing sales to competitors while at the same time bolstering your own product.
1. popout window, no status or toolbars and no resize - keep window size specific to the product information. If the visitor really wants the other product they must close window, leave and find them, and
2. Add this content to a PDF > downloadable, a take-away and print friendly version that allows visitors to digest the info > of course your contact info and links are on every page making the "buying" potential easier.
Be honest and objective > the purpose is to show your strengths against their weaknesses, but these considerations MUST be true.
Why? > human nature > most of us are comparable shoppers and even moreseo online since all competition is just a click away (at the search engine) if they really want to compare > you can't stop them thus providing the added value of "in one place comparing" makes it more appealing to remain at your site.
Off-line, ever notice that duracell is right beside EverReady, Levi's next to Lee's, or a different perspective - Macdonalds, Burger King, A&W, Wendys, etc. are all in the same big parking lot...
1 product or 1,000 products you will never appeal to all, therefore the added value to what you do offer, and openingly comparing this is enticement > creating the desire to buy.