The short answer is that the 770 HP is the more powerful. However, I suspect the question is about the difference between power and torque. 'Torque' is the rotational equivalent of force and if an engine is exerting a 'high torque', it's pushing hard. This occurs when the vehicle is accelerating, especially from rest. 'Power' is the rate at which energy is used and is related to the rate at which an engine consumes fuel. So, accelerating from rest is a high-torque, low-power situation. Conversely, a vehicle running at high but constant speed would be a low-torque, high-power situation.
Different types of engine have different abilities: steam engines and electric traction motors produce maximum torque at low speeds, i.e max torque at almost zero power. Internal combustion (I.C) engines don't work well at low speeds and maximum torque occurs at a different speed from maximum power. This is why you need a clutch in an I.C engine power train.