If you take the time to find out how many hits it takes to kill a person you will find out there are Three catagories they fall into.
Small weapons, heavy weapons, and even weapons.
This was tested only in multiplayer, so similar ratios would depend on the level you are playing with.
Heavy weapons are the Rocket Launcher, and the Sentinel Beam; they kill in three standing melee attacks, two moving attacks, and one jumping attack.
Even weapons are the Energy Sword and the Brute Shot; they kill, no matter the type of attack, in two melee attacks.
The small weapons are all the rest of the weapons; they kill in six standing melee attacks, 3 moving attacks, or 2 jumping attacks.
Standing attacks are standing still, and hitting the other individual. Moving attacks are when the two bodies are in motion to each other, either one or both bodies. Jumping attacks are melee attacks made during a jump.