Although I think Michael McIntyre would do a fine job for Williams this season..., this is one of the most difficult questions of the year!
The first three GP2 champions (Rosberg, Hamilton, Glock) have all shown an aptitude in Formula One, Georgio Pantano didn't when he was there, but ART seem to be able to pick a driver! Also, Hulkenburg won by quite some distance, whether due to Romain Grosjean's promotion or not remains to be seen.
Barrichello is surely going down the slippery slope to retirement. He didn't look very good for large parts of last season, with a couple of excellent wins thrown in. He was, however, failing to beat Button from hugely promising positions, such as in Interlagos.
On the basis that I think Barrichello may be down, I go for the Incredible Hulk.