My main gaming group likes Disposable Heroes which uses pre-calcualted armour equivalents in discrete zones and hides the math to the end user. However, if I were to create that system from scratch would be to add a probability curve to the shell penetration values rather than a linear increase in multiples of d10 pips.
On the other hand, my other group likes Bolt action where there are 6 classifications of armour (Softskin, Armoured Car, Light, Medium, Heavy and Super-Heavy).
Personally, I prefer Disposible’s method of doing it, since there is less arguing about where you put your curve for grading the tanks and it’s more time-frame independent. A T-55 in 1950 has more or less the same front plate thickness than t-55s in 1991, but I would argue that compared to the competition, it drops from a heavy to a medium over time.