They are basically digital booster packs, so the newest sets have the more valuable code cards, but they are all pretty much worth $0.20-$0.50. The code cards that offer special things like avatar items or extra cards are worth more depending on what they give you.
If it gives you an avatar item: you won’t sell it.
If it gives you a specific, meta-relevant card: It will likely go for more than the typical code.
Also, the staple value tends to be 30 cents per code, with bulk deals leaning towards 20 cents and the newest set sustaining an extremely brief value around 45 cents.
Oh yeah Gary, if you want to trade the codes for cards or sell them, let me know. I’ll try to an arrange a trade/sell for you. I just need to know how many of each you have.