This is my futuristic Empire of Greater China flag.
This flag displays the territories that are the three regions of the Empire of Greater China. The Qing flag is included at the top because they consider themselves as the heirs of the old Qing empire despite having no relationship to the dynasty. It is not a monarchy. It is a cyberpunk society where the government has a traditional Asian aesthetic in terms of art, architecture, and clothing, but also uses high technology very heavily. The government is ruled by a committee of wise philosophers and scientists.What is the reasoning behind including all of this on one flag? If it is set in the future, why the Qing flag as well?
I'd agree for modern Coats of Arms but I think noncrispiness suits flags as it reflects rendering at a distance and moving.I generally prefer vector graphics programs like Inkscape or Illustrator for flags since you do want it to be crisp regardless of resolution. Inkscape is pretty much free so it's one of the best programs for flag or logo making, imo.
As others have said, it depends how complicated you want your designs to be. For something simple (just stripes maybe with a few stars or similar) then Paint or another simple program is fine. A better bitmap graphics program like paint.net will give you more options and more control over what you do, by letting you use different layers, etc. If you want to resize objects without losing detail, then it's better to use a vector graphics program such as inkscape. (There are other programs, obviously - those are the two I use, but if you use a Mac you might need Gimp instead of paint.net for example.)