I really enjoy Socialist Realism paintings, because they’re more subtle propaganda and more art than regular propaganda.
As for disparity between styles, I find it interesting to see what poverty does to propaganda. While the Soviet Union, China and Yugoslavia were relatively prosperous for communist nations, North Korea, Cuba and various African countries were not, and for this their propaganda took a hit. You see a lot more hand-painted billboards, a lot more slogan-based propaganda that’s quicker and cheaper to make, and a lot of smaller displays instead of grand structures and monuments (North Korea being the stand-out here because they decided to put propaganda and military far above other economic needs so they can still afford giant statues of Kim Il-Sung and Jong-Il). At least that’s my take on it from what I’ve seen, I admit I have no idea about art history so I can’t tell you if certain countries drew influence from one area or another.
Thanks for the questions!