I just graduated and am now involved with a (non-commercial) project where we are in the design phase.
I am using Visual Paradigm Community Edition to draw sequence diagrams since this was the tool I used in my uni classes.
I am not asking where to or not to use UML diagrams. I am asking which are the best tools to draw them.
It is free and online. I can draw diagrams that I used to draw with Visio but I don't have to install software and can use it from anywhere.
I can export the documents to my local machine as a master file (e.g. file type is *.drawio) or can export them as an image (e.g. JPG, PNG, etc.)
There are lots of subjects that you can turn on (also free) ranging from architecture to electronics.
I can usually find what I need or something that works well enough for my simple needs.
I can also use it kinda like a white-board in screen-sharing meetings.
Though - looking at other comments - yEd looks pretty powerful. I'll have to check it out.
+ free + online no instalation needed + source is text file can be put in git for collaboration
- source is text file no drag&drop
I am using it quite often to sketch LoFi mocks.
It stores in your browser's localstorage, and you can easily collaborate with others in realtime.
I opt for https://draw.io if I need a quick diagram personally (it's a big plus that you can guarantee the recipient has access since it can be opened from the browser version).
We used to use Prezi. It is pretty amazing.
If you are using UML during design phase, you probably are not going in right direction.
for the design phase I think the C4model and a sequence diagram provide all the tools to think about your project.
in order to produce such diagrams you can use plantuml. Because that way you can store it with your code in git.