Usually discount codes are better than free dining in deluxes. It really depends on how good the percentage off is and what you need. Hopefully they'll release the general public discount codes for the rest of the year in a month or so as it looks like it's only up till October right now.
Also a lot depends on what you already have or are getting. If you already have tickets to use then it would be more expensive to buy the passes that you would need for free dining (although you could use those passes at a later date as long as you didn't activate them). We usually do the 35-40% room only discount code for a deluxe room, buy our tickets from undercovertourist.com using the Mousesavers link, and then pay OOP for the two TS meals a day we eat.
And, yes, if there are still rooms available at the resort you want that are associated with the discount (i.e. free dining or discount code) you can just call and apply whichever one saves you the most money. However, they only block out so many rooms with each promotion so you would need to call and have it applied as soon as you get it/see it. Even if there are rooms "available" or you have one reserved, it may not mean that there are rooms available with the free dining or discount code anymore.
