Both OA and Comodo firewall/HIPS are rated very highly whenever there is a comparison. And run well with Avast! I used CFP for about a year, but only on one computer because I found it to be demanding in terms of maintenance and reconfiguration. But very configurable and capable after taking the time to learn and beta test it. OA is much more usable, but perhaps not quite as configurable. OA has some features that are very useful for mobile wireless users, such as the Firewall Status Display and its treatment of network interfaces and computers in the paid version, so it ended up primary on my mobile laptop as soon as it was available for Vista. Some of the ongoing issues with Comodo were virtually impossible to get fixed (like logging, SPI, the "ASK" function, installation/removal issues, ...-see their forum for long threads), since they were/are working their own agenda leading up to the Suite activity. Even implementing Bugzilla for prioritizing bug reports and the various bug forums got nowhere. Tall Emu, OTOH, seems to make sure that user inputs are tracked and corrected as they go through the build process. I even got a few changes incorporated, rather than having to put them on a wish list somewhere. I think part of this is because OA is still working on building a great FW/HIPS and uses a conventional closed/open beta cycle to do incremental upgrades, rather than surprising the users with the "big bang" that is primarily features vs fixes and has variable testing beforehand. So I switched my main computer to OA also, and have been beta testing the latest versions for them. Along with Avast!
But ultimately it is up to you, the features you value, and how you monitor and maintain your firewall/HIPS.
BTW, HIPS is now, but some of the behavioral programs show promise for more reliably keeping your computer clean in the future. If you read the Wilders forums, especially
http://www.wilderssecurity.com/forumdisplay.php?f=30, there is a lot of interesting stuff going on. But will probably mature about the time the next generation of malware shows up.