I find pivotal tracker to really be my sweet spot amongst all these offerings. Maybe I just didn't know how to use it but Trello seemed a little too simplistic. What do you like about Trello vs. PT?
The other problem with PT is that it promotes a bottom-up view of your project rather than a top-down view. You end up missing the forest for the trees. With Trello, I can create a list for a high-level goal like "Validate that users want the features we're building" and then list sub-tasks within that.