They need (IMO) an experienced driver and a young talent. So my choice is Barrichello and Grosjean. Why?
Barrichello: Is way more comitted to his team than Raikkonen. I reckon that if the '12 Lotus is a good car, he can still do the job. Remember 2009, he was almost out, like now, and returned to win two fantastic races, and could've won his home race for the first time.
Grosjean: Is, was and will be a Renault driver. He has always been talented, but unlike 2009, he is much more prepared now. This is the time for him to race a full season.
Why not Raikkonen, Petrov, Senna? Raikkonen doesn't seem keen on returning, he seems to want to race anywhere, not necessarily F1. Petrov is simply a jerk. Just take a look at how many races he spent behind Heidfeld in the standings
while he was not racing. And Senna is talented, but irregular. He is in the Q3, then goes out and crash, then he barely makes it to the Q2, then he does an outstanding race, and so on.
Stats: 139 Starts / 7 Wins / 9 Poles / 5 Fastest laps