datacoin will be the best
Datacoin is based on Primecoin's proof-of-work. Primecoin doesn't look too healthy right now but it's still far more active compared to Datacoin. Unless OP specifically wants to use Datacoin's data storage feature, it would probably be better to mine Primecoin instead. After all, it's the same algorithm.
Also, since DTC's dev abandoned the coin, it might be a good idea for someone else to step up and hard fork it so that it's merge mineable with XPM. That way, DTC would benefit from the extra hashpower and there wouldn't be two projects trying to do the same thing (i.e. finding prime numbers).
