It depends really on your play style.
Since howitzers became out of meta I prefer Fortified Armour Doctrine over Jäger Armour, because the command p4 is more useful against Brits so you can engage late game tanks longer.
Lightning War doctrine is also very nice because it has a Tiger and the Stuka strafe, which helps a lot when dealing with late game armour. Since you get also g43 on your grens it's one of the doctrines that allows you to fight on even ground in urban close combat maps. This makes it also harder for your enemy to escape the Ju87 strafe and close combat neglects the range advantage tank destroyers have over your Tiger.
I personally also love spotting scops, since it gives you a huge advantage when having it upgraded on a 222. Especially with vet it becomes a maphack, very useful on a lot of maps.
Great information. I too really love spotting scopes. I think they are the best underused upgrade. I have never regretted getting one, especially on a stug.