I personally would go with the Sonicwall. It's a dedicated security appliance, hardend OS, plus the security features of antivirus, antispyware, and intrusion prevention all at the gateway level (subscription is required for the security features).
The problem with Linksys, Belkin, D-Link, etc... routers is that they are built for the SOHO market. They were never built with the intention of more than about 5-10 users and to operate under heavy loads for extended periods of time. That's what you'll get with commercial grade equipment like Sonicwall, Cisco, Watchguard, Juniper, Fortinet, etc...
I'd be looking at one of the TZ series boxes with the wireless-N built in. Buy hey, that my opinion.