First off, all characters are different in the Books and Movies, and that includes Smeagol/Gollum. The split, to me, is better 'visualized' (Duh!) in the Movies. I read the text where Slinker and Stinker debate their plans for Master and the Fat One, but it's Peter Jackson's camera angles and Andy Serkis' facial expressions that really drives home that this creature is truly mad. Though going into TTT I of course knew that Smeagol and Gollum were internally at war, but even so, PJ's delivery of this war made me almost think, for a moment, that there truly were
two creatures.
Like Boromir in the Movies, Gollum here is slightly more sympathetic. And the Henneth Annûn beating of Smeagol left me thinking that anyone involved deserved whatever treachery they received. Ouch! On the other hand, when Smeagol plays the happy puppy, I'm a little put off as I still see the creature as rarely being comical - unlike dwarves, which are the buffoons of Middle Earth.