Here's my favorite's list that I like which aren't either against policy (have to have my flag mod lol).
Expert AI 2.0 Africa Add-on - This makes those terrible Sahara battles be gone by making those parts of Africa impassible but at the same time not bad looking as they are sort of like Integrated puppet area's but they cannot be passed through.
Expert AI 2.0 - Better AI Template building, I'm not sure what else it does but the other nations kick my but once when I turn their difficulty up even to medium which is awesome
Colored Buttons - Makes the different tabs such as production and such stick out better in the UI
Expanded Technology - Industry - Equipment 1.3.1 - It doesn't add a ton of new units or industry but it adds enough to make it more immersive and fun plus I like a bit more diversity.
More Theatre Icons - Lets me differenciate more in my Theatres as they can get clogged when I'm using my smaller specialized armies such as Armor, Mountaineer, Marine, etc.
World Tension Balance - The WT goes through the roof with the SCW and if Japan takes China Quickly the USA sometimes will be able to get into the Allies in 1940
Better Terrain View - Easier to differentiate terrain types
Strategic View Adjustments - Easier to see in Air Mode where planes or, same goes for fleets, and also Cities stand out better, it just looks better overall for me and being able to find Air wings and Fleets quicker is a big improvement.
Those are just a few but my biggest thing is reducing minor's division spam, I do like Vanilla + as it increases the combat width making room for more specialized division templates, I also just hate fighting in the Sahara, it has irked me since release to see divisions there even if the AI doesn't send as many anymore. At least with HOI4 you don't have partisans spawning in no infrastructure area's though