I don't know about "best", but OmniGraffle has been a staple for many years:
There may be more sophisticated software through these search engines*:
- * Links to my pages may give me compensation.
the chrome web store has a bunch of other free tools like this as well
-*links to my pages may give me compensation
I'm using the free yEd for these and a lot of similar purposes - unlimited screen size, good PDF export, works great with huge organizations:
Hope it helps
mayI add not mentioned crossplatformed tool ConceptDraw PRO with huge template galery for ERD, UML, ORM, flowcharts, etc. I’ve tried omnigraffle and conceptdraw, they both do a good job but conceptdraw seems to be more powerful. What i found interesting they provide their own office suite for mind mapping, project management and diagramming that works with ms products via xml.
In a combination with Conceptdraw Office this drawing tool can do much more than expected from the charting software, like live dashboards, visual reporting, interactive and smart mindmapping and infographics.