First of all, I suggest you to update your question's title by replacing 'best' with some more appropriate word. The reason is rather simple: IMHO, whenever one is asking about something, using terms 'best' or similar, he/she should specify corresponding criteria, since potential answers might/will be very different, depending on those criteria. In the lack of specifying criteria, such question doesn't make much sense and, thus, cannot be answered. Secondly, questions, asking to recommend software with a comparison twist, usually strongly imply people's opinions. Such questions typically are frowned upon on StackExchange, in general, and on this site, in particular (though, there are numerous exclusions from that "standard" approach, which often makes thongs quite confusing). Thirdly, software that you mentioned in your question belongs to the class of mind-mapping software, which is quite different from general diagramming software. All the above-mentioned points are not to criticize you, but to establish some context for the rest of my answer.
While previous comments and answers mentioned some good general diagramming tools, such as Dia, yEd and GraphViz, I am very surprised that neither you are aware of, nor anybody has advised such extremely popular tools for publications, especially in the engineering context, as LaTeX and various relevant LaTeX packages. I highly recommend you to take a look at such packages, as
tikz (pretty much, the gold standard for LaTeX diagramming),
smartdiagram. They, as most things, related to LaTeX, have rather high learning curve (especially
tikz), but for many people and applications the time and effort spent are well worth it. In order to support and illustrate my recommendations, feel free to take a look at my Ph.D. dissertation defense presentation slides, which I have prepared with the help of all packages, mentioned above (and then some). For the general LaTeX-based diagrams, please see slides 15, 16, 17, 21, 23, 25, 27, 35, 40, 44 and 51.
A couple of examples from the presentation (for those not wanting to leave this site):
Final note: in many situations, especially in research and engineering context, a very significant benefit of using LaTeX-based approach is the ability of automating diagrams and other resulting artifacts generation. This aspect is IMHO very important from the reproducibility perspective.