Pz3 and the KV1 would be nice. Both common tanks that made a large impact on the earlier part of the war we're concerned with. But much of this depends on the Pz4 itself. Will there be the early marks with short barrels, or the later ones with long barrels? Or both? Because without that long 75mm gun, I can't see how a KV would work. And in any case, that Pz3 is going to struggle against anything. Gah... it's tricky to pick with so limited a number of tanks!
That said, I still definitely think it's better to have fewer well modelled tanks than lots of poorly represented ones. The tank system in RO1 never felt up to the same level as infantry combat. It would be nice to see them on par.
i plussed you there cos back when stalingrad was announced, and i thought of tanks these 2 came to mind and they are favourites.
I even had a p3 ext model (various marks) with half a mind on HoS.
i thought the KV1s would match best with slightly weaker armour but still lies the problem of a dual purpose gun giving more flexiblity due to inf support than the L60 50mm of a later p3. P3N can support infantry but will get hammered by the kv1 (or t-34 of course).
THe best balance might be 2x piii J and 1 Piii N vs 2 x kv1s.
The same applies to the P4 - i think they are planning on an F2 or G at first - makes sense to use a dual purpose gun for parity - but that weapon is a jump up in AT capability so in itself might swing the balance from russ to ger quite sharply.
However use the inf support version and it will be vunerable if alone against armour.
what is clear is that the setup of maps , objectives, re-inforcements etc can fine tune balance so we needn't worry about inherent tank advantages - i trust TWi and the decent mappers from RO to get this right. As the game matures you'll maybe see plenty of maps where one side only has armour, certainly where one side has more.
What does concern a bit is the monkeys who are going to make crude open tank battles without considering (or having the capacity to understand) gameplay - that's where complaints could start coming.
oh and stug is an absolute must as said.