Both good games, but I think AC2 is by a good margin the better game. Also, as was said earlier in the thread, AC2 is made for the console, DA is not. Be prepared for some fucking frustration with the console version of DA. It's essentially a run-of-the-mill RPG with lots of problems and bugs. BG3, except crappier. Assassin's Creed 2, on the other hand, is incredibly polished and smooth as shit. While it's obviously a sequel, and as such not incredibly innovative, it still is very much its own thing, and is fairly unique.

Then again, if you're in an RPG mood, DA might be the way to go.