All the models that you listed are good for a small office firewall/vpn server. I used the 800 series routers in some of my small branch offices as a firewall and site-to-site vpn router (the features are of course based on the software image you purchase with the router). The PIX 501 is just as good and is designed to be a firewall and vpn server. Most of my shop has their skills based in Cisco IOS, so we chose the routers over the Pix firewall. You should checkout their website because there will be certain features that one will have that the other won't and vise versa (one being a router and one being a dedicated security device). As far as problems, I have not run into any problem with my 800 series routers. They are programmed just like any other routers. Cisco just released their SDM (Security Device Manager) 2.1. Which allows you (if you are not familiar or don't want to use the CLI) to program the VPN, Firewall, etc from a GUI (this applies to the router).