Slitherine

Some people think one should pick a set of Traits and use them for everything.
I disagree, I think Traits should be selected for each DLC as best fits.
I am not using negative traits as challenges, but picking ones with minor situational effects.

I have not used 'Trophies of War' before and thought it would be a good time to try it out.
I have used SlwMod before and with a little bit of planning it is not a problem.
This AO campaign I decided to use ToW, FlxCmmd, and SlwMdrn throughout the whole war.
Additional traits picked for each DLC as they seemed to fit.

Since one may capture a lot of Art DndArt is a minor handicap here.
It allows picking KllTm and BttlAcd.
Since AOSCW start with a green army, and AO39 with green Infantry, BttlAcd is a way to pickup quick experience.

Difficulty: General

SCW
Traits:
Killer Team
Flexible Command
Trophies of War
Battle Academy
Slow Modernization
Denied Artillery

AO39
Traits:
Killer Team
Flexible Command
Trophies of War
Slow Modernization
Inefficient Supply

AO40
Traits:
Infantry General
Panzer General
Master of Blitzkrieg
Killer Team
Flexible Command
Trophies of War
Slow Modernization
Denied Artillery
Denied Air Force

DndArt blocks Stug3B, and DndAF blocks Me109F which are minor issues.
Me110 and Ju87 upgrades are not necessary.
The weakness of the Russian AF may allow DndAF in AO41 as well.

People already talking about 1941 expectations.

I personally don't like to engage with the General traits that much. I think my current 1940 run uses Trophies (I need that prestige on Generalissimus), Terrain Expert, and the negative of Arrogant (just to try a new one out). I think this is because while some players have absolutely 'min maxed' the system to pick the least negative damaging traits to afford the most beneficial positive ones... I'm not sure this is representative of the majority of players. Even as crazy high prestige levels have become lately, some people are still finding themselves running low. There's no way those players are picking up all (any?) of the prestige orientated General perks. lol

The Denied X traits are the most obviously abusable ones in the DLC campaigns (Killer Team is the only one that is comparable, as getting up to three super heroes permanently for a temporary cost is immense), but that possibility does add an opportunity cost to Auxiliary Force; if you pick Denied Air Force to gain 3 easy trait points, you won't be able to leverage Auxiliary Force to maximum effect, i.e., no flooding the battlefield with half a dozen extra fighters whenever you wish.

As far as difficulty is concerned, the highest ones should require some degree of min-maxing.