My preferences is Smoothwall, and never had any problems so far.
True, Smoothwall does have fewer "out of the box" options than IPCop, but you can always add extra functionality if you want to do so.
From what I've heard, the community at
Smoothwall is more active than the IPCop forums.
But it all boils down to what YOU think and feels is best for you.
I like Smoothwall better because it allows me to tinker with it, adding extra functionality should I require it.
For example, I've setup three Smoothies for clients so far :
All have the Dansguardian content filter (block out pr0n sites), and ClamAV antivirus filter.
One have DHCP enabled for both green and orange (it's for a PC shop) thus enabling the technicians to connect virus-infected PC's for online scans without fear of disrupting the other network segment.
The other one runs the mfilter implementation of the
dspam statistical mail filter which is designed to block spam. The current implementation uses greylisting which cuts spam down with an impressive 99.99% success rate. Only drawback is that it is currently only scanning SMTP inbound. This one also runs the Guardian Reactive Firewall which blocks bad IP adresses automatically.
On the last two I have installed the Bandview mod, to enable the operator to keep track of bandwidth used so far.
So far I've never had any serious or major downtime with any of these.
But the feature of switching automatically over to uncapped accounts is a nice feature, and one which Smoothwall does not have, you'll have to initiate the switchover manually.
IPCop is a fork of Smoothwall, which means they share some roots.
Regards
Libs