Like: Fogbugz (small-ish team), Trello (small team)
Don't like: Jira, Whiteboard (like.. literally a whiteboard)
Want to try: Zenhub
Don't like: Jira, Whiteboard (like.. literally a whiteboard)
Want to try: Zenhub
TBH, though, I struggle to find any other meaningful negative differences.
My biggest peeve is that management always want to configure it to do time-tracking. This makes engineers hate the tool and lie to it, making it useless for bug tracking.