Offensive Suicune can attack right off the back. +0 Leftovers Hydro Pump 2HKO's many things, such as Scizor. It is also bulkier, and has Leftovers. It just has the perk to boosting itself.
Marvel Scare is all cute and nice, but its not like it would appreciate a burn, a paralysis, or Toxic. It isn't defensive, it is offensive. At least Pressure can mess with Heatran and random Hydro Pumps.
Offensive Suicune is just better. Its faster too. :(