I haven't pre-ordered it yet either. I would probably pre-order on Steam, unless you can get bonuses through other sellers, but still obtain the key on Steam. Steam will most likely have the earliest fulfillment, as in, release day you already have it pre-downloaded and it unlocks. Similar to how GTA5 was released. You were able to download it a week beforehand, so on release, after the game is unlocked and files checked, you can play. 
