We've used Bugtracker daily for the past eight months. It's intuitive, has tons of features and does the great job for our team of five. We are opening it up to a larger group shortly. It does lack the auto-response, but being open-source you can add this feature. The code to do so in available but I haven't made this patch yet. It's highly configurable, especially if your tsql skills are average. There's also a excel export if the reporting is an important consideration. All in all I'd go with Trac, for the Project management/wiki features, but I'm in a .net shop so this works out well since the skillset to manage the system is inherent. Best wishes.