Hi I'm Murder, I'm the kind of guy that likes to know the mechanics behind the game and doesn't mind doing a bit of research.
Today we will be looking at combat levels, how each combat stat affects your combat level and therefore whats the fastest way to combat up. I know alot of people will claim training defense is the fastest way to combat up, well Kappa in the chat boys because this is a load of bullshit.
Combat stat - combat gained - levels required to get a combat level
Range/Mage - 0.5 - 2
Att/Str - 0.33 - 3
Hp/Def - 0.25 - 4
Prayer - 0.125 - 8
Now obviously only your highest offensive stat will affect your combat (mage/range/melee)
To avoid confusement melee = (att + str)/ 1.5 ie. 50 mage = 75 melee stats ( like 30 attack, 45 str)
Now if you disagree with any of these numbers feel free to drop a comment, but I think they are all right as -> https://youtu.be/l2CCAsnz_g4?t=59s