"My experience with Cutler Hammer CH and Square D QO breakers has been far fewer failures do to plug-on connections than with loose/stripped/cross-threaded connections when using bolt-on breakers."
My experience is exactly the opposite! I've seen many plug-on breakers that have burned the breaker and buss bar beyond use. But I've never seen a bolt on fail.
If the bolt-ons are loose or stripped that sounds like a workmanship issue. Bolt-ons are definitely not as "user friendly", but that really shouldn't be an issue for a pro.
