Operations Manager for an IT company. We have quite a few clients who still rely on Windows 7, totaling about 300 computers total. The other 2,000+ workstations have already been converted to Windows 10 with no complaints whatsoever. Believe it or not, some clients still use Windows XP and Vista. The biggest complication with upgrading is that there's several, proprietary software developers (mostly for the industrial industry, i.e. the computers running assembly lines, maintenance equipment, etc.) who haven't jumped on the Windows 10 bandwagon yet. Employees NEED this software to work. So it's a gray area where the software developers need to do their part to get their software running on Windows 10 before we can jump in and perform the upgrade.
With Microsoft discontinuing security updates for Windows 7, we'll be upgrading those 300 computers to Windows 10 by the end of Q1 2020, which is a nightmare. On a personal note, I've had no issues with Windows 10 and I see no reason to not upgrade ASAP. Antivirus software won't protect you if your operating system is missing critical vulnerability patches, which will only be available in Windows 10. It may seem like a hassle, but it's worth it.