I would say, If you are going to sell the cards, it would be best to sell them in a set. People are more likely to grab at them to get some of the hard to find cards. Especially if they are new and don't have a lot of cards. However, if you have some really valuable cards such as;
Galadriel's Silver Ewer and
Gilgalad, HKotN, I would sell those as single cards. It wouldn't necessarily be a good idea to sell the commons and uncommons as single cards unless they are really rare like
Rapid Reload. Not many people will buy a card like
Hobbit Party Guest as just a single card. If you have handfuls of copies of commons and uncommons, I would suggest selling them in a lot. People grab those too because they never know what treasures will be in there. Out of all the cards the ones from Hunters to T&D are by far the most valuable. Hope this answers your questions.