I've been using clarkconnect for several years now and I have been very happy with it. I host many services from my house and clark makes it VERY easy. If all you need is a firewall/router any of those distros will work just fine (m0n0wall, smoothwall, clarkconnect, ipcop, etc). If you want to host a website, email server, vpn server, or many other things clarkconnect is a very good option
Clarkconnect probably has the highest system requirements of the bunch but if you only have a couple users (or arn't running all the services) a PII will work just fine. My friend's clark box is a PII 233 with 256mb of ram and it works like a champ.