If you are going for lowest possible price confirmed seats go straight for fly confirmed for even less.

Use delta.com or kayak.com to find the lowest possible ticket price. Then plug those flights into the fly confirmed for even less template and you will get the discount on the lowest priced tickets you could find.

Typically the lowest price tickets are non-refundable anyways so nothing is lost by using the non-refundable fly confirmed for even less option.

Stay away from the "refundable" fly confirmed for less.
While it sounds like those ticket are refundable, that's only true if the pre-discount fare basis was refundable. If the pre-discount fare is non-refundable, then the fly confirmed for less "refundable" ticket is also non-refundable...

Most likely you aren't looking at full fare refundable tickets anyways if you're asking about the discount program ;-)

It's a great program to knock some money off a confirmed ticket when you can't afford to play roulette with non-reving...

Cheers
George