The basic idea of Planetary is that there are weird and wild things that happen just behind the veil of the everyday, and the PCs are superpowered individuals who seek these things out; perhaps to exploit them, perhaps to protect them, but mostly because they are there. This doesn't have to be Wildstorm, and I really don't want OCs; what's the fun of playing someone else's character?
I think freeform would be the easiest, unless someone else wants to GM -- you do not want me to GM something.