I installed Comodo last year and hated it. All I want is a lightweight, easy to use firewall which won't keep bothering me. This drove me to distraction with its constant messages and complexity. Uninstalling it was a nightmare - Vista security centre was still reporting it as active after I had removed it.
After many hours of sourcing information about this, I finally managed to get rid of it by re-installing, uninstalling again using Revo Uninstaller (deep scan mode) and then using a batch file supplied from the Comodo forum.
Even then the 'fun' wasn't over - the batch file had disabled the security centre and when I restarted it was not monitoring my AV so I ended up reinstalling it. All is OK now but I really can't do with companies who make their products so hard to remove.
If Avast would care to develop a firewall that is lightweight, simple to use, and not take up a sizeable proportion of the computer's CPU then I would be happy to use it. For now, I am sticking with Vista firewall, the one in my router, and the firewall provided by my ISP at their end. It must be OK as so far I haven't had any infections (using Avast which I like enormously and Defender).