I did not see Forgetting Sarah Marshal so I actually have never seen Russel Brand in any movie. I will say that he was pretty quick witted yesterday.
Sarah Marshall was really funny. Plus, it has a topless picture of Mila Kunis in it (yum!). There are a disturbing number of scenes which feature Jason Segel's junk flopping around, but Mila and the chick who played Elle on Heroes are hot.
Plus, it's really funny.