Making a beaufitul demonstration for your work is very important when you want to bring a clear and interesting message to the readers, especially in academic community.
Thanks to a lot of drawing tools, both open source and commercial, both click-to-draw and code, one can make beautiful and informative piece of artwork that provides better information to enrich the quality of a manuscript. Let us have a look of all available tools out there.

1. Matplotlib, Matlab and similar tools:
   When doing scientific works, it’s pretty sure that one would know Python or Matlab or other programming languages (if not, don’t worry, those languages are not difficult to learn and use). They provide powerful tool to make neat, clear, vector images which can be inserted easily into the documents or presentation. One drawback we might have is that they’re all code, so we need to learn and imagine a little bit about the result we’re aiming for, or we must repeat the modification of the code until we reach a satisfied resulting images/plots.
   Fortunately, a lot of examples have been provided on those officical sites of Matplotlib and Matlab, so we just go there, copy the code and manipulate them with our data.
2. Illustrator, Inkscape, AutoCAD, Photoshop
   I prefer this approach when I have to prepare illustrations for my presentation/manuscript. They are WYSIWYG image editor that we can create and export to whatever format we can, they are versatile. One should know which programs is for vector drawing and which one is for rasterized drawing (Photoshop). Combining with the scripting tool provided with each of them (Python and Javascript), one can achieve automated tool that increase the productivity of their workflow drastically. Moreover, AutoCad provides lots of powerful engineer tools (surface area calculation, inertia moment…), combining them with clipboard tool to paste into Word like BetterWMF, one could make a neat document.
3. LaTexDraw
   Final option I can propose is LatexDraw, a tool that uses the Tikz drawing capacity inside latex. One good thing about this one is that artworks will have a script version that one can paste directly into latex document and they can always be modified later, directly in the latex document, no need to revisit the original image. Also, LatexDraw can export some commons format like PNG and EPS that is greatly useful. Also, LatexDraw is crossed-platform since it runs on Java, so you can draw your image on your windows laptop at home, bring the file to the linuxa work station at work and continue the work without any problem. Finally, since it’s Latex, we can insert math equation however we want, this utility is useful especially when to want to do some annotations for mathematic illustrations.
4. draw.io
   In my opinion, this free app (both online and offline desktop version) is the best among the charting apps. It makes other paid-app funny.  Other paid-apps charge you more than $10 for  something similar, some are worse as they requires subscription. Draw.io is totally free and powerful.

Some notices:
Avoid using JPG, they are lossy format.
Always prepare a B/W version of your plots/images since most of the time people print the papers in monochrome.