We have previously used Sophos and Fortinet, but they are very complex, difficult to maintain, and not user-friendly.

I have been using since Fortigate Firewall in my previous company, When I joint my current company here is already deployed Sangfor Firewall. It's a pretty similier interface as Fortigate Firewall.  

I have experience with Fortinet firewalls and compared to them, Sangfor is cheaper and easier to implement. That said, we did not use FortiClient, or any other solution as our VPN.