Omnigraffle is by far my favorite, unfortunately only available on Mac OSX. I use Windows more lately and struggled to find a comparable offering. Then discovered Lucidchart https://www.lucidchart.com/ and have grown to enjoy it quite a lot. It offers common Cisco and AWS networking icons, and has some nice exporting options and the auto-expanding canvas. There are some quirks but it is cheaper and in my opinion cleaner than Visio.