Of all of the discount-related addons, the Discount Coupons and Gift Vouchers addons are the most popular. They generally serve the same purpose but there are important differences that should be noted since only one can be installed and working at one time.

Here's are explanations of each:

• Allows adding or subtracting discount - Adding a coupon is nice if you want to charge for some extra service. Something like,
  
  "We are offering a free $10 product with each order. All you have to do is pay an additional $1 in shipping. Use this coupon code to do that."
  
  If you only want to have negative coupon codes (giving discounts), then you don't need this option.
• Can sell codes to customers - Allows a product, like a $10 Gift Certificate, that a customer can buy and send to someone else to use. If don't want to sell gift certificates, then you don't need this option.
• Offer codes to new customers - When this option is used, when a customer creates an account, they will receive a coupon code for some percentage off.
• Track usage
• Exclude products/categories
  Both versions have the above two options but Discount Coupons handles them a little better.

There is an additional package available for each that will allow a coupon code to be generated and sent to the customer with their order. This is a common tactic used by many sites to keep customers coming back. They place an order and then receive a coupon good for X amount off of their next order.

Please let us know if you have any other questions regarding the differences of these two addons.