Is the default firewall that comes with the Fedora distro safe enough on my Fedora firewall-router box , or is it better to run a dedicated application like Firestarter ?
The only other service I run on my firewall is the cups server for my /dev/lp0 printer connected to it.
tia

Firestarter is simply a Graphical interface for configuring iptables (the standard linux firewall), so it's really the same thing. Iptables is argueably one of the more robust and effective firewalls available. However, I'd recommend doing some research on how to actually configure your firewall first.

I understand that both applications are based on iptables, but Firestarter has more options, like ICMP filtering and NAT enabling that are not present on what I call the "default firewall " ( KDE->system settings->Security level )
So, is one easier to crack than the other ?
Is there any Linux firewall applications rating ?
After reading the Redhat v9.0 documentation chapter about iptables ( imho one of the best short articles on the subject ) I didn't feel like rolling my own rules.
Thanks for the info but I was expecting a reply like: A is better than B, or both are crap use C instead

If Fedora still uses lokkit, than by all means use a better front-end (Firestarter, Guarddog, etc). lokkit is the worst firewall I've ever seen, for any OS--ever.

I'm not really a big fan of lookit either. But if you're going to use something configurable like guarddog/firestarter, just make sure that do some port scanning/ pen-testing after setting it up.

Also, guarddog is designed more as a strict packet filtering firewall, so if you need any routing capabilities (NAT/Masquerading/etc), you'll need to install it's companion app called guidedog as well.