For personal projects, Trello or Asana are about right in terms of complexity.
For organizations larger than about 3 people and engineering teams larger than 2 people I strongly prefer to track software work to be done in something explicitly designed as a bug database, with visible and short numeric identifiers for work items and a strong preference for a Kanban view. Jira is almost perfect for this, though it's a misery to configure, a little bit overkill for teams at the smaller end of this scale, and its few shortcomings are very short indeed. Phabricator will also do in a pinch. Pivotal is nice in principle but lacks sorting and filtering features that make the backlog possible to manage.
Getting non-technical people to look at the issue tracker on a regular basis is crucial but nearly impossible. I'm still waiting for someone to build an awesome integration between JIRA and Trello or asana.
I've found complexity and/or/aka too many features discourage adoption, this was particular painful when a previous company I pushed to purchase Axosoft quickly abandoned it - nobody (including me eventually) could be bother using it. Hence easy to use, easy to get going, 'where 90% is intuitive' tools like Trello and Basecamp, arguably deficient in many formal project management areas, continue to attract and maintain customers. Combined with skype, hipchat or private slack for realtime communication seems to solve most of the headaches. A client recently added freshdesk to the mix too, again for 90% its intuitive.
The simpler tools definitely encourage adoption. On a larger project I work on, we use Rally - most abominable platform I've had the displeasure of using - solely because the project manager is able to assign "points" to user stories, which translate to hours of work per story. Hence, when a dev is at x number of points, s/he's at y% capacity for that sprint. We tried Jira but without being able to assign capacity, ruled it out. I've heard good things about Basecamp...
I've spent the last couple months working on RowStack (http://rowstack.com). It's still in beta, but we're working hard on it, and looking for feedback. Let me know what you think (matt at rowstack.com)
For organizations larger than about 3 people and engineering teams larger than 2 people I strongly prefer to track software work to be done in something explicitly designed as a bug database, with visible and short numeric identifiers for work items and a strong preference for a Kanban view. Jira is almost perfect for this, though it's a misery to configure, a little bit overkill for teams at the smaller end of this scale, and its few shortcomings are very short indeed. Phabricator will also do in a pinch. Pivotal is nice in principle but lacks sorting and filtering features that make the backlog possible to manage.
Getting non-technical people to look at the issue tracker on a regular basis is crucial but nearly impossible. I'm still waiting for someone to build an awesome integration between JIRA and Trello or asana.