I enjoy a plain red flag, it strikes as powerful to me, only needing one colour that everyone bleeds, no national symbols this or cultural ones that and the meaning of it when being flown by the Communards of Paris. With that being said, I do like the flag of Burkina Faso (both visually and in symbolism), the Soviet Union and I have a soft spot for the flag of the Tuvan People's Republic.
I, for fun, sometimes make flags. (I usually follow the rules of Heraldry when making them, for I think they are better. Don't follow Reddit crap, they are shit. Fuck 'Good flag, bad flag' even the committee that made that garbage letter disowned it for how shitty it was. Ruined a generation of flag designers.)