For attack value, Inf/Art is more cost effective than Inf/Arm, no matter how you roll the dice (or don’t :roll:)
Spending 56 IPCs on Inf/Art gets you 16 land units, with a total offensive punch of 32. (dPunch also 32)
The same spent on Inf/Arm gets you 14 land units, with a total offensive punch of 28. (dPunch of 35 though) This force is more skewed and thus keeps fighting better after the first round of casualties, however the skew is not as advantageous of the higher unit count of the Inf/Art force.
However, the Inf/Arm force is still superior IMO because of the mobility of the Armor units. Mobility can’t be accounted for in all the number-crunching, but it is a key aspect of the game. And it doesn’t change from LL to ADS. If the game was simply two territories fighting for control of two territories directly between them, Inf/Art would be the way to go. Unfortunately, A&A requires maneuvering. So you need mobility - force the enemy to defend multiple points, or retreat.
In addition, the Inf/Arm has better defense value. Since it’s overall a better combination, that’s what I prefer to load my TRNs with.