I'll say Demon's Souls. Although I admire Dark Soul's open world atmosphere, Demon's Souls atmosphere is definitely more gritty.

Dark Souls fixed an enhanced a lot of things from Demon Souls and its a bigger game so my pick is Dark but please do buy Demon, both games are the best thing on PS3.

They are both fantastic games, and would highly recommend playing demon's souls. what everyone says is true, just 1 more thing i would like to add, I found that dark souls' equipment system (can hold as much as you want), encouraged one to experiment with weapons a lot more. i played around with long swords, curved swords, axes, spears, etc. whereas with demon's, i always stuck with my trusty falchion and beefed the hell out of it.

Loved playing as a Wanderer in both games. I enjoy being nimble on my toes paired with destructive power, than being a heavy holding some mammoth weapon that makes the buster sword look like a pencil...

Rosie Stark says, "Come here and let me shoot you in the face." Demon's Souls (and probably Dark Souls, but not played it yet) are the best games on PS3 AFTER Valkyria Chronicles.

Demon's Souls maybe. They are slightly different, both worth the play through (although, if Demon's Souls servers are down it won't be as fun.)

Demon's

Dark souls' difficulty is unevenly distributed, the day-to-day adventure is easy thanks to estus flasks and bonfires while the bosses crush you like an ant (ornstein & smough anyone?)

Demon's Souls i found to have a much better atmosphere and feel to the game. The nexus was stunning along with other locations and i found the story to be much easier to follow

Dark Souls; it's more balanced.

I've finished Demon's on standard and new game +, while in Dark Souls I've only played the first portion of the game, so far Dark Souls seems more difficult to me. Since everyone says Demon's is harder, probably the second half of the game or New Game + is easier compared to Demon's Souls.

edit: On topic, I can't really judge since ? haven't finished Dark Souls yet, but they are about on par I guess. There are enough gameplay differences between the two to avoid the feeling of repetition playing both games.

Another thing that makes Demon's Souls better is the unique World Tendency mechanic where lots of things in the game would be accessible only under certain circumstances. It was difficult to understand but that just made it even more awesome in my opinion.

It was a really unique and fantastic feature that I missed not only in Dark Souls (it retained a similar principle but to a much lesser extent and not dependent on the multiplayer situation) but wish other games would have copied by now.

I never understood why the extremly hard difficulty of this franchise is actually seen as good. I bet if the games had an average difficulty they would have a 10 points lower meta each. I've played the first one for about ten hours and it was pretty mediocre to me, despite of how boring it is to die over and over again.