By 2020 I'd kind of hope we're sending mostly-autonomous humanoid robots. Wouldn't that really inspire people's imagination? And they could start building the infrastructure for a colony.
I wouldn't want to seriously see humanoid robots as the first workers on Mars. The human body isn't terribly well-shaped to perform the kinds of tasks needed in an efficient manner. Balance, for example, is monumentally tricky and doesn't need to be with a four-wheeled style robot.
2020 is not very far away, definitely not far enough away to make a large robotic advancement in time to make it flight ready.
Why "humanoid" robots? Why not just "robots" that can do a job no matter what they look like?
If nothing else, PR value. And to inspire new engineers.
If you want PR value, send flesh and blood humans. Otherwise send the tool that's best for the job.