Del Sur is “Green” built so there are features that make your home more energy efficient (Solar panels on some homes, Tankless water heaters etc). Del sur also have multiple parks with pools in them (all gated) for all residents to use. These two things are reasons that I would love to live in Del Sur.
Del sur is also only on one side of Camino Del Norte, a huge advantage IMO. I hate that about 4S. I wish 4S had an entrance like San Elijo has on the south end. It makes it feel like its own city. But whats done is done.
4S will give you more diversity in home plans/sites/prices. You are also within walking distance to shops/restaraunts/ LA Fitness and closer to a major highway artery. You can also go two different ways to get to the 56/Carmel Valley.
I think both are in for a deep downswing. They have both already seen a drop, but more is on the way.