Messi and Raki on the bench, no use risking them since the start (who knows maybe Neymar, Suarez and Iniesta can win it on their own anyway), and Roberto deserves his first 1st Clasico eleven this year anyways, even more so with Messi and Raki being not fit for the whole match. They can enter around 60-70 minute (like Messi did against Atletico last season), IF we're chasing the result in that stage, otherwise i'd prefer to not see them at all, if i'm being honest.
I'm thinking some form of 4-1-2-1-2 could work really well from the start (Bravo; Alves, Pique, Vermaelen/Mathieu, Alba; Mascherano; Sergi Roberto; Busquets; Iniesta; Suarez, Neymar). With shifting throughout the match, for example Roberto moving ahead to RW to put pressure along with S and N on Madrid's shaky defence, while Iniesta operates on CAM behind them, while Busquets moves back along Mascherano on CDM to cover for Roberto. so that would be like some form of 4-2-1-3. Then Messi comes in for Roberto, maybe Rakitič also for Mascherano or Vermaelen/Mathieu and we play the last half hour with that standard lineup to close out the game.