I have played all the way through the 3 DLC's on a fairly easy setting and am now going through again on a slightly harder setting
(Still only the middle default one)
Things I have noticed....
Never bother with recon, it always gets killed, this is the opposite of what some have said.
Don't bother with anti tank none of it is any good
Likewise don't bother with anti aircraft either.
My strongest element is air, build up to 3-4 stukas and 3-4 me109's This early in the war you don't even need to bother escorting the stukas, losses are rare and the ME109's have very good ground attack capability. Always kill all enemy aircraft as soon as they appear.
Joint 2nd strongest element is infantry and artillery. Towed artillery is very effective, infantry are generally very effective. I keep tank numbers quite moderate, they are useless against infantry and whilst ok against tanks stukas are even better.
I am assuming once tanks progress to the Panzer IV F2 or better this will change and I will increase the armour content a little. I increased it a little once the Panzer III F and Panzer IV D became available as at least these have some capability. Panzer 1, 2 and 38t are mostly useless, stukas are far more effective.
Love the DLC's looking forward to 1942.