Hard Enamel this means you will have a smooth surface going from the metal outlines across the colored enamel. These are the best looking designs and most professional. It becomes flat and smooth from the layering of the enamel and a hard buff at the end.
Soft Enamel this will leave the metal outlines raised above the enamel that fills the the colored areas. This is a cheaper and some prefer this look. Another option you could ask your manufacturer for is an epoxy cover over the soft enamel: that will make it smooth but also raised above the entire design. This is a design that many older vintage pins have.Sandblasted and 3D - these designs do not lay any enamel into the design but still maintain recessed areas where it would normally sit. This is an option for very clean and solid designs that do no depend on the colors to set it off. They often can be found as 3D as well, meaning they are not just one level of metal but actually sculpted.
Printed this design has an epoxy layer on top to seal a printed image inside. This is a less used option by most independent creators but it’s perfect for images far too complex to be turned into an enamel pin.
There are other additional options some manufacturers offer at an extra cost.
Screen Printing this is done on top of a hard enamel pin that has a smooth surface.
Numbering - perfect when you are doing a limited run of a design. If you are creating a limited edition design your customers are trusting that you will not be making more of this exact design and exact coloring. The value of these types of limited runs often make the pin worth more in the future especially if your designs become highly sought after. Be good to your audience and do not recreate this exact design if you make a limited edition run.
Back Stamp this is a great chance to put your logo on the back of your pin so that anyone can find you in the future. It is worth the investment and manufacturers often won't charge you again even on other designs for the back stamp because the mold is on file.