I like plantUML, I really do. but I think more people will be attracted by it, if they improve design and colors, so it looks modern out of box without any hacking
I was originally a proponent of it, but I find these days i prefer Mermaid. It doesnt hurt that there are more Markdown editors/viewers integrated with Mermaid than PlantUML.
Until mermaid comes up with the vast list of diagrams one can create in Plant UML, I don't see it as operating in the same weight class. E.g., wireframes, basic Gantts, AWS diagrams, component diagrams with graphviz (thought I confess I hate this dependency), archimate diagrams if you're really hardcore.
for UML it seems mermaid is indeed good enough, I used mermaid but never used it for OOD UML, after a quick read it looks very simple and straightforward for UML comparing to plantuml, especially you can embed mermaid right into markdown as text
You could customize a style for your diagrams and then include it via a one-liner in every diagram you create. This also allows for branding of diagrams.
Personally, I'm a huge fan of the simplicity and whenever I present such a diagram to teams or execs, I break the ice by warning them it'll be "ugly" or "let's go back to 1995 for a sec" :) More importantly, the focus remains strictly on the content because of the basic design.
