Spec ops is the commander I use most of the time.
The Stg 44 upgrade allows you to counter shocks and greatly increased the potential of wiping squads.
The command Panther is better much at destroying tanks than the KT since it has mark vehicle and is fast enough to chase enemy tanks to finish them off. Recon flares are much harder to notice for your enemy than a recon plane and thus work very well with a Stuka. Infiltration nades allow you to clear buildings, which is what okw usually can't really do and it punishes blobber, likewise wipes Riflemen that use hit the ground.
Luftwaffe doctrine allows you to rely on falls in situations where you can't get obers like when you have to go first T2 flak track then t1 for healing and a jagdpanzer. Volks and sturmpios just don't work after 15 minutes if you face allied elite infantry.
Additionally they kill snipers when popped our correctly.
Valiant assault allows you to chase tanks with your volks or kiting snipers. Luftwaffe assault gives you a free squad when you are low on manpower and the strafing stukas pin and kill enemy infantry, very useful in late game vp struggle games.
A commander is about what it gives that you use often, I would rather get the infiltration nades from Scavenge because the doctrine helps me get shreks out faster and more reliably. And Fallsch while good units on paper suffer from the fact they cost a massive amount of MP and have very little health and armor. You are better off just getting a either infantry from another doctrine or just more volks. Valiant Assault is good for tank chasing but ultimately is a munition dump mid game that could be better spent on shreks, imho.
The Commander Panther might be better than a KT a AT on paper as well, but in the current IS2/Jackson meta it's just going to get raped if it gets attacked by a IS2 and friends, I would much rather have a King Tiger which will bounce shots of it's armor and has enough health I can retreat it and repair it with out some insane micro.
On the subject of the StG44, the killing in cover and better close range is good but at 90 munitions you are better off giving a volks squad a shrek and using Infiltration nades if you need to clear an enemy out of cover.
In terms of usefulness from personal experience Jadg > Fort > Scavenge=Spec Ops > Luftwaffe > Elite Armored.