you have to see in the long term. Which one will go up in the future? For me it is Datacoin...
Datacoin is a Primecoin clone - why to mine datacoin when u can mine Primecoin instead? For me XPM is the way to go - many other CPU coins already have GPU miners released.
Because one is very easy to mine while the other is not. I believe Datacoin will soon rise so it gonna be more profitable than primecoin considering primecoin's diff. For me DTC is the way to go cause it is indeed a fork of primecoin which is one of the best coins but can also be used for decentralized data storage! So it has double use