He is a better choice than Senna IMO.
How do you know? From 170 odd GP starts Heidfield has, he's never won a race, and he's been in competitive cars over the years.
Senna had to drive a clown car last year, so we've not seen his full potential in an F1 car. What F1 needs is the oldies to retire (it hurts to say it) but Trulli, Barrichello, Schumacher and Webber should retire.
We need more young daring drivers like Hamilton, Kobayashi and Alguersuari that take risks and push the car to the limits.