Help needed with web content filtering

Considering hardware options, such as Watchguard SOHO or SonicWALL SOHO firewalls, as well as software options such as Proxy-Pro Professional Gateway for a proxy server for our 24 user LAN using a T1. The objective is to be able to keep some users totally off the internet, and to deny other users access to certain types of internet sites such as porno, violence, etc., and ideally being able to check out a log showing how much time they have spent on browsing the internet and what sites were visited. Besides the firewall security benefit, the content filtering part is the most important thing I’m looking at. Any advice or information on how well each of these solutions work as efective filters?