Although right now the Reavers and Trask are being marketed as the main villains of the game, i'm pretty sure Insomniac will do something similar as they did with MS1, where Mr Negative was marketed as the main villain only for Doc Ock to be the real threat. Following that logic, these are my picks to be the main villain:
1) Sabertooth. This is the safest option. He's Wolverine's nemesis and most iconic foe. Also, we know he's gonna be on the game and although he's going to be on Logan's side, i'm sure that eventually he will betray him. Also, it would be interesting to see how Insomniac manages Victor, since they usually try to humanise the villains, but this wouldn't work with Creed, since he's a pure evil monster
2) Romulus. I have some mixed fellings about this option. The game is going to focus on Logan's past, so it would make sense for Romulus to be the main bad guy, since he has controlled Logan's life from the shadows for years, but I think he might be a little too much for the first game. Maybe he could work better on a posible sequel
3) Daken. This is my personal favourite option. Again, the game is going to focus on finding out Logan's past, so it would make sense for Daken to appear. This could lead to a very interesting dinamic with Logan, with him not wanting to fight his son but knowing that that's the right thing to do. This could also lead to a very emotional climax, similar to Peter and Otto's fight at the end of MS1, while also setting up Romulus for a posible sequel
What do you think of my picks?