You should mention your tow vehicle, and if you plan on using rails, puck system, or turn over ball mount type hitch. It will help determine what hitch will work best for you, such as the one pictured using the Ram puck system.
To answer your question, some 16K models may be adequate, an 18K is available, as well as the 20K. Some think it is best to buy a hitch to fit the trucks capability, rather than the FW you are buying. If you have a newer diesel DRW, you may want a 25K hitch.
Jerry