In my opinion, Dark Souls is way better. I recently started playing it and was instantly hooked, the game is incredibly hard at first, and even when you do get the hang of the game it's still hard. I'm level 25, played a total of 24 hours, and still haven't rung the second bell.
I love Skyrim too, and the new Elder Scrolls Online looks great. But if it isn't that great I'll probably only play a few months. But I'm more excited for the new Dark Souls 2 game.
So which game series do you like more?