When comparing Dia vs yEd, the Slant community recommends yEd for most people. In the question“What are the best flowchart / diagram softwares?” yEd is ranked 7th while Dia is ranked 8th.
Ranked in these QuestionsQuestion Ranking
Pro Free and open source
Pro Tons of icon sets
Has flowcharts, uml, chemical engineering, electronics, and dozens of other complete sets, built in.
Pro Custom gzipped XML format
Pro Completely free
Runs on Windows, Linux and Mac OSX. There also is a Web application.
Pro Automatic Layout
With automatic layout you get great looking diagrams with very little effort. yEd has the most versatile and most complete collection of automatic layout algorithms.
Dia has not been updated since 2009. It's already a very complete piece of software, but still sad.
Con UX is a joke
UX is not good enough. For example, to edit element text you must double-click it, then click text box, and then you can start typing text.
Con Not free-as-in-freedom
Not released under an open-source license.