The Romanian Commander adds +1/+1 defence not +1 cover.
There’s not much to compare, they aren’t the same class of ATGs.
The 8 Pounder isn’t that good; it’s obselete (Russian ZIS-2 is the same stats for less), and it can’t hurt heavy tanks. Two of them are more expensive than a PAK 40 (+4 points). with only a moderate increase in firepower. They’re best used to support 17 Pounders (which is really what you should be comparing the PAK 40 to), or to take on medium/light tanks. The PAK 40 is a serious threat to all vehicles at all ranges. The only disadvantage of it is tying up 14 points in a defence 3/3 soldier. But it at least gets 4+ cover to help it survive. With the popularity of heavier tanks (Pershing, Tiger, King Tiger, IS-2, and most importantly the KV-1 with Cossack/FO/etc) the PAK 40 is simply the better choice. But again, it also doesn’t make sense to me to even be comparing the two; it’s like comparing a bolt action rifle to the MG 42 and asking what’s better.