Earthships are a good solution for single, self-sufficient houses or smaller villages in remote places, not so much for whole cities. Personally, I like the design and the idea behind it, but the best part is the very clever integration of heat-regulation, wastewater treatment and other useful devices directly into the building. And it's all realized with "low tech" means. Our houses could have been constructed similarly, but there was no need for that because people didn't care about the energy-efficiency.
Masdar City is an attempt to create a self-sufficient city with a high-tech standard, but also by including useful low-tech elements like
windcatchers.
However, I'd still prefer to live in an earthship rather than in Masdar City because they are more individual and constructed by motivated people and not oil sheiks with a huge budget. On the other handside, I don't want to talk down the potential value of Masdar City as an experiement for future self-sufficient cities or even arcologies. It just looks incredibly sterile to me.