The front should be somewhere between soft and medium. When I say a "soft" front I mean softer than the rear.
Here's the rational.
When you launch, typically you're going to have enough torque to break the tires loose no matter what, so the idea is to get as much of that torque applied anywhere you can. A lot of the torque will be applied to moving the car forward, but anything extra will usually cause tire spin, unless you can store it elsewhere (for use later).
There are a couple places you can store torque. One of those places is in the sidewall. This is why bigger and softer sidewalls are better for drag racing.
See the stored torque?
That sidewall will unwind at some point down the track when you can use the torque. Also while you're wrinkling up the sidewall at launch it helps cushion the blow to the contact patch preventing all of the torque from being applied all at once, which helps the tire hook. It allows a more gradual application of torque than you'd have normally.
Now the same thing is going to happen in the front suspension. When you launch the car the front will rise up a bit unloading the tires, which is bad. Too much front lift obviously hurts traction, but hopefully you have the back stiff enough and enough weight over the front that you don't lift too much. Having the front a bit on the soft side allows the front to lift a bit, storing more of the torque in the suspension for use later, and maybe more importantly preventing 100% of the driveline torque from shocking the contact patch into loosing traction.