I also have more than five years of experience with Fortinet FortiGate. I have worked with models such as the 30E, 50E, 60E, 100E, and 60D. I also have experience with the Meraki Firewall.
The VPN limitations are better with FortiGate. Even with the lower versions, such as the 30E, it supports 100 tunnels and 100 users. With SonicWall, you are limited to five IPSec VPN connections at one time.
FortiGate also supports DynDNS, which is an important feature for smaller companies.