[xpil]

What drives me absolute bananas is the way they changed licensing for Visio. You could get the database reverse-engineering feature (Pro version) for a fixed, one-off price up to some point. Now it's all subscriptions. Blah.

(great software though, I have to admit)

As for the main topic, my favourite diagramming tool is GraphViz, mostly because it is easy to script / automate, does a great job auto-placing things, handles large diagrams quite nicely and works on any OS.