Without getting into bloat issues of Monero, or Darkcoin instamine, a PoW coin, if actually able to achieve anonymous transactions, is in a difficult position. Governments would regulate against it, and PoW mining data centers are large attack vectors to be legislated against or just taken over. Yea, they would be located in many countries, but governments seem to cooperate a lot on things like drugs, so they might cooperate on issues like this too. I guess you could say Bitcoin sort of faces this issue as well, but they haven't made any big moves against it yet.
On the other hand, and without getting into why PoS is making the big holders even bigger, PoS coins are not secure since Governments can achieve to hold 51% of coins by using some gag orders on the exchanges without anyone ever realizing.
I wouldn't touch DRK with a stick. Nodes can be attacked easily by an adversary with the required resources, the initial instamine thing and the name... on the other hand Monero has ring signatures which I trust a lot more.