Let see both these coins
ARK Coin (ark.io)
Ark project is an actual project , they have thought out their issues and are very honest with how they answer the issues. It is a shame that why I have missed this project before. With that said, please note I am talking about their concept and the technology. How much would ark value after 1 year ? no one knows but they are not a scam as in not here for a short term. They are actually in the game with their concept, the concept is to kind of provide a ready-to-go blockchain so anyone can make their coin out of the ark ecosystem.
A coin is good if the vision on which it was built is strong and legit. Aurora coin punch line is "Auroracoin is an opportunity for Icelanders to free themselves from currency controls and government debasement of the currency." While it is based on Litecoin.
So why they couldn't use Bitcoin or Litecoin itself ? why go for a new coin ?.So I wouldn't go much into Aurora as its an ordinary coin with a weak vision