thats a hard one. if i had to chose between 2 i would pick Dragon Age Origins. you can design the character anyway you like and can act however you want. the storyline is addicting to stick to. the second one would of been Mass effect 2. both of them are by the Bioware company.
DA:O is an awesome game, but lacks customization. NWN2 is awesome, similar to DA but more options, if you combine the two games in either of their toolsets using or replacing the erf files you get some awesome gameplay and it looks amazing
you have to agree the graphics for Dragon age can't be beat if you have a top notch computer. if you have a great computer put the setting on high sometime