L.A. Noire. Portal 2 is a worthless overrated piece of stuff that doesn't deserve half the attention all the mindless forgets on the internet give it is great (apparently) I just wasn't that pumped for it's release as everyone else is. Infact, the day portal 2 came out I pre-ordered Dungeon Siege 3.
So, go with L.A. Noire if you want a long and fun experience and Portal 2 if you want a moderately lengthy explosion of amazement.
I dunno actually, I don't have either (:s) and isn't L.A. Noire still in development?