I platinumed Uncharted in a few days and the online didn't really appeal to me so I traded it in and got Batman which really looks like a keeper so far, lots to do and maybe a few too many riddler thingummajigs to find but it's quite addictive working out how to get them once found.
I haven't tried Dark Souls yet but it's one of those games that I'll leave for now and pick up when it's cheaper as I haven't been drooling over it like I was with uncharted and Batman.
Skyrim looks massive but it looks too massive for me, I used to love games like that but now I just find them overwhelming.
So, I would suggest Batman. Or go the route that I did and get Uncharted, platinum it real quick (crushing is pretty easy with only a few times that made me want to throw my controller at the TV) then trade it back and grab Batman.