For the easiest thing in town, I'd say "Atlassian Jira"�https://www.atlassian.com/opensource/overview

I am using Fogbugz and JIRA on several client projects and JIRA definitely has more traction and engagement.

But, migrating may be less painful than before:�https://confluence.atlassian.com/display/JIRA/Importing+Data+from+FogBugz+for+Your+Server

https://www.atlassian.com/software/jira/importer-migrations#!jira-fogbugz


Phil