in this series i attempt to use math to find which units are most efficient. The rules and limits I impose on units and the math are as follows:

only 1 command ability allowed
cost of battalions and buff units are not included in the calculations for efficiency
when there are random values I use the average roll
I round to the nearest 2 decimal places
effective wounds are calculated with this formula: (wounds per model/chance to fail a saving throw). this number is not accurate against attacks that deal multiple damage 
5+/5++ denotes a 5+ save with a 5+ ignore damage save (such as deathless minions)
I do not take into account abilities that trigger on rolls of 6+.

Units That Synergise With It

Astrolith bearer (reroll hits)

skink priest (reroll saves)

Saurus Oldblood on Carnosaur (+2 attacks with a single weapon)

Saurus Oldblood on foot (reroll wound rolls of 1)

How to Use the Unit in Game

One interesting thing about the Oldblood is that the “best weapon” for him changes depending on whether or not he is buffed. The points per damage calculation for each weapon will take into account the jaw attack. Here we go:

Unbuffed offense vs 3+ save:

maul= 0.66 (155.84 points per damage)

warblade = 0.57 (176.47 points per damage )

spear= 0.66 (155.84 points per damage)

greatblade= 0.66 (155.84 points per damage)

jaws= 0.11

Ubuffed offense vs 5+/5++

maul= 0.72 (139.53 points per damage)

warblade= 0.76 (133.33 points per damage)

spear= 0.72 (139.53 points per damage)

greatblade= 0.72 (139.53 points per damage)

jaws= 0.14

Buffed offense vs 3+ save:

maul= 2.04 (53.81 points per damage)

warblade= 1.32 (79.47 points per damage)

spear= 1.71 (63.16 points per damage)

greatblade= 2.28 (48.58 points per damage)

jaws= 0.19

Buffed offense vs 5+/5++

maul= 2.24 (48.19 points per damage)

warblade= 1.75 (60 points per damage)

spear= 1.87 (56.6 points per damage)

greatblade= 2.5 (43.64 points per damage)

jaws= 0.25

Defense: 7 wounds, 4+ save, ignore rend -1

unbuffed vs

rend 0/-1 = 14 (8.57 points per wound)

mortals = 7 (17.14 points per wound)

Buffed vs:

rend 0/-1= 28 (4.29 points per damage)

mortals= 7 (17.14 points per damage)

Honest Goblin