There are three different kinds of bonus experience in Dead Island.
The first is bonus experience from breaking limbs. This is possible via blunt weapons and fists.
The second is bonus experience from cutting limbs. This is possible via sharp weapons.
The third, and last, is bonus experience from head-stomping fallen zombies.
Additionally, this bonus experience is scaled based on the level of the zombie, and is also affected by some skills in the characters skill trees.
There are a lot of prefixes and even more questions about them and their meaning. Some have only been seen in pre-release info or screeshots and some effects have not been well documented. There's a fairly good list on the Dead Island wiki and while it's a bit unreadable, the weapon mod FAQ lists the prefixes under the associated mods. Neither of these consider mods unique to one weapon as adding a prefix for the most part. If you can follow the association of the prefixes to the mods, the Dead Island wikia has some more detailed effect information. The accuracy of any of these sources is somewhat dubious for the effects so it may take some digging into the games' files for something more conclusive.
As you know, the game takes a base items and then adds prefixes after to modify characteristics. The game uses a weighted random algorithm with the item level as the base value to generate items and it is possible for items to have multiple prefixes. There are also prefixes from weapon mods that can be added and others of unknown origin.
I'll transcribe the known prefixes (107 at present) and their believed effects, ordering the generated prefixes according to the game's data file and I'll add whether I believe the descriptor is positive or negative:
Name Effect
Defective -Accuracy
Skewed -Accuracy
Imprecise -Accuracy
Flawed -Accuracy
Unreliable -Accuracy
Short range -Accuracy
Semi-accurate +Accuracy
Well-balanced +Accuracy
Calibrated +Accuracy
Accurate +Accuracy
Precise +Accuracy
Trusty +Accuracy
Spot-on +Accuracy
Perfect +Accuracy
Dead Eye +Accuracy
Feeble -Damage
Puny -Damage
Mediocre -Damage
Ordinary -Damage
Spiteful +Damage
Malicious +Damage
Damaging +Damage
Dangerous +Damage
Savage +Damage
Vicious +Damage
Cruel +Damage
Slaughtering +Damage
Devastating +Damage
Deadly +Damage
Lethal +Damage
Flimsy -Durability
Frail -Durability
Shoddy -Durability
Fragile -Durability
Weak -Durability
Worn -Durability
Used -Durability
Reliable +Durability
Dependable +Durability
Sturdy +Durability
Stout +Durability
Strong +Durability
Tough +Durability
Impervious +Durability
Indestructible +Durability
Tiring -Force (may lower handling?)
Frightening +Force
Striking +Force
Threatening +Force
Debilitating +Force
Awe-inspiring +Force
Formidable +Force
Terrifying +Force
Disabling +Force
Shattering +Force
Enervating +Force
Crippling +Force
Incapacitating +Force
Paralyzing +Force
Diabolical +Force
Sluggish -Reload
Slow -Reload
Unwieldy -Reload
Languid -Reload
Medium-speed -Reload
Brisk +Reload
Rapid +Reload
Quick +Reload
Swift +Reload
Deft +Reload
Speedy +Reload
Fast +Reload
High-speed +Reload
Super-quick +Reload
Lightning-fast +Reload
Critical Crit +?
Weighted +Damage, +Force, Crit +4%
Shark +Damage, +Force, Crit +6%
Heavy +Force or +Handling or +Force, +Damage, -Handling, Crit +4%
Piranha +Damage, +Force, -Handling, Crit +4%, Bleed out chance
Barbed Bleed 1, Crit +4%
Bleeding Bleed 1, Crit +5%
Naild Bleed 1, +Force, Crit +4%
Bolted Bleed 1, +Force, Crit +4%
Glazed Bleed 2, Crit +4%, Bleed out chance
Razor Bleed 3, Crit +4%
Slash Bleed 3, Crit +4%
Sawdisc Bleed 4, Crit +6%
Explosive Explosion 2
Burning Fire?
Striker Fire 1, Crit +2%
Scorching Fire 1, Crit +4/5%
Phoenix Fire 2, Crit +6%
Pride Impact 1, Crit +1/2%
Impact Impact 1, Crit +4%
Lightning Impact 2, Crit +4%
Magic Wand Impact 3, Crit +4%
Tesla Impact 4, Crit +6%
Detox Poison 1, Crit +1/2%
Paralyzing Poison 1, Crit +4%, Disabling chance
Venom Poison 2, Crit +4%
Toxic Poison 3, Crit +4%, Corrosive chance
Deathstalker Poison 4, Crit +6%
Shock Shock 1, Crit +1/2/4%
High Voltage Shock 2, Crit +4%
Short-Circuit Shock 3, Crit +4%
Old Smoky Shock 4, Crit +6%
There are still a lot of unknowns pertaining to the prefixes. I've seen the burning prefix shown in screenshots, but I'm not sure if they've actually been found and exist within the game or if they were part of the pre-release screens. It is listed on the wiki so I added it, but information on these is scarce. There's also the question of effects on handling as few of these seem to provide their clear effects on it as the critical mods seem to reduce handling and the tiring prefix has been described as doing this as well, but the effect is hard to corroborate.
Best Answer
It's actually five different mod's:
Each mod requires 5 diamonds to craft, which means you will need 25 diamonds to craft every single one of them. So I would recommend keeping them until you have enough to craft them all.