Justin Mitchell- Designing Products at Sofriendly.com
Lucidchart is without a doubt the best in my opinion. It's fast, simple, complicated when you need it to be, and supports full collaboration and sharing.
Jeremy Bauer- Writer + Arts Instructional Designer
This one's pretty easy to use. It also has tons of integrations—Slack, G Suite, Box, Microsoft Office Suite, Dropbox, Jira, etc— and has mobile apps. I've mainly used it to map stories for writing projects, bit it's a pretty robust tool with a lot of different use cases.
Mike Coutermarsh- Code @ GitHub
Definitely Lucidchart, has been around for years. Tons of features, works well/easy to use. Can't go wrong here.