What is the most polished OSS ticket system?

I am particularly interested in solutions that do very well creating ticke开发者_如何学Cts from e-mail, and that allow replies to be sent back and forth via e-mail in a threaded fashion.

While I don't think I'm qualified to say which is the most polished, I would definitely say Redmine is very competitive in that area. http://www.redmine.org

We recently began using it in our department and the most frequent comment from the users has been how clean and usable the application is.

While I don't think I'm qualified to say which is the most polished, I would definitely say rt is worth looking at. We've used it in a company of about 40 - 60 people for IT and related issue tracking. I rate it as extremely easy to use, our sysadmin thought it was easy to install and configure/