An outboard is more critical than an inboard. The only reason one may be more critical is in the event of a crosswind. On a crosswind takeoff, to stop the aircraft weathercocking into wind, 'downwind' rudder must be applied. So if an upwind engine failed, there is less rudder authority to counter it as there is already some applied to counter the swing due to the crosswind. That's it. Not a serious problem at all, there is usually plenty of authority designed in to counter this. It's more theoretical than practical.