R – Which bugtracker works best with Eclipse’s Mylyn on Windows server

Why don't you simply use your original Bugzilla instance?

Personally, I'd consider it tedious and useless to separate tasks and bugs.

Bugzilla, Mantis or Trac all work just fine with Mylyn. I would say that the best one supported is and probably will be Bugzilla, since eclipse people use it for their own bug tracking, and Bugzilla connector is developed by core Mylyn developers.