Imp - You bring up some valid points in regards to knowing the enemy's stuff. I do know that there were individuals in various contries that preferred the armerments of their enemy, but I also know that they were probably few and far between. Although, the stories I hear in regards to the Stern SMG that you Brits came up with say that almost everybody that was handed a Stern would try to find anything else, even German arms as soon as possible, with the MP 40 being the preferred.
On the flip side, I do know of a German commando officer that appartently preferred a silinced stern to just about anything else, so it goes both ways.
It stands to reason that most resistance units whould fight with "enemy" weapons as they would be the easist to get. If you look at Partisan units in the Yugoslav OOB (and I believe in the USSR OOB as well) many of them use Kar 98s and other german small arms. It makes sense that if you needed guns and ammo it would be a lot easier to steal them off dead soldiers/ammo dumps/weapon supplies than try to get the supplies out of the supporting country, whether it was partisans and the USSR or the French resestance and the UK.
PatG - Also some valid points. In my experiments I haven't given them T-34s yet, but generally the older, lighter models. I think I once looked at a section of BTs in one go and a T-70 in another. Nothing heavy (no support) and nothing in large numbers (mainly one or four AFVs total.)