ORIGINAL: 76mm
I find recon rather problematic for several reasons:
1) Why is it that only recon planes can fly recon missions? While I understand that you don't want to allow entire air fleets to fly recon missions, it seems odd that all fo the other thousands of aircraft can't see anything. As Soviet player, I've had many turns where I've gotten ZERO recon flights in particular areas, and I have no idea why.
2) Again, as Sov player I'm rather surprised how often I have virtually no idea where entire panzer armies are, despite doing as much recon as I possibly can. You would think that reporting the locations of panzer and mechanized units would be a rather high priority taks for partisans, so maybe such units within a few hexes of a partisan unit should be detected. This would also give greater incentive to develop (for Sovs) and squash (for Germsns) partisan forces.
I agree with the problems on recon. One additional issue I have is that recon seems far too strong for behind the front lines, particularly as far as the Germans go. Historically throughout the war (but particularly in 1941), the Germans rarely had an idea when and where (or for that matter that they even existed) the Soviet reserve formations would appear--- Glantz's Barborossa Derailed has good examples of this. My sense is that recon is far too strong for anything 3-4 hexes beyond the front line, giving the Germans an ahistorical strategic advantage in 1941---- you may not be able to tell exactly which specific divisions are there, but one can tell by the mass of counters where the Soviet armies are and where their next line of defense is going to be, leading to little chance of unwelcome surprises for one's panzers.
I think the Soviets should get an advantage in long range recon, particularly after 1941, tied to both partisans and far better strategic level intelligence then the Germans ever had (Gehlen's apologias aside). Even in 1941, it's striking how detailed the Soviet knowledge of the German OOB was, as evidenced again in the summarized daily reports in Glantz's Battle of Smolensk book, which repeatedly show fairly accurate information down to a divisional level or below, and a good and timely sense of the movement of German reserves.