I've been using PlantUML and Mermaid for my own diagrams.
Mermaid is quite basic; it lacks functionalities that for me were necessary; for example, direct connection between attributes of different classes.
All in all, PlantUML seems superior to Mermaid, at no cost (both languages are relatively simple to learn).
Mermaid is supported by Github, which may be a necessary requirement for some. On the other hand, among the many functionalities, PlantUML's JSON is unusually good looking out of the box, and if one required the diagram it outputs, it's a great feature, because it requires no syntax knowledge.
Both PlantUML and Mermaid mostly produce (Mermaid more) ugly-looking diagrams (dated, to say the least). In PlantUML, this problem is compounded by the explicit lack of layout, by design.
Other warts: both (PlantUML and Mermaid) languages have limited comment support - they are only supported in specific locations of the diagram declarations.
D2 could be a very welcome "next gen" diagramming language. However, the devil is in the details - text-to-diagram.com show a very basic functionality, so one must carefully check the requirements.
Regarding text-to-diagram.com:
- there's a mistake - PlantUML does support rich text (although "rich" is a fuzzy definition)
- class diagrams are an important use case, which is currently missing
EDIT: clarification about the comment limitations.
Mermaid is quite basic; it lacks functionalities that for me were necessary; for example, direct connection between attributes of different classes.
All in all, PlantUML seems superior to Mermaid, at no cost (both languages are relatively simple to learn).
Mermaid is supported by Github, which may be a necessary requirement for some. On the other hand, among the many functionalities, PlantUML's JSON is unusually good looking out of the box, and if one required the diagram it outputs, it's a great feature, because it requires no syntax knowledge.
Both PlantUML and Mermaid mostly produce (Mermaid more) ugly-looking diagrams (dated, to say the least). In PlantUML, this problem is compounded by the explicit lack of layout, by design.
Other warts: both (PlantUML and Mermaid) languages have limited comment support - they are only supported in specific locations of the diagram declarations.
D2 could be a very welcome "next gen" diagramming language. However, the devil is in the details - text-to-diagram.com show a very basic functionality, so one must carefully check the requirements.
Regarding text-to-diagram.com:
- there's a mistake - PlantUML does support rich text (although "rich" is a fuzzy definition)
- class diagrams are an important use case, which is currently missing
EDIT: clarification about the comment limitations.