I'm no expert, but aside from slack our team has found that most of these platforms have complicated on boarding and a cumbersome learning curve. Although these platforms are good in there own sense, I concur with Ivana Kingston and Brigitte Kobi. There is no perfect solution as of yet.
The one platform our team has started using is https://jixee.me/ it has both Slack and Github integration points and it was very simple to get started. This might not be the solution for every team, but for ours it's been working great and I believe it's a step in the right direction. I definitely would recommend this platform as well.
Name: Jixee.me
Elevator Pitch: Jixee is a task and issue tracker for development teams. We are the best alternative to JIRA.
More Details: Early stage. 1-10 employees.
Looking For: Feedback.
Little late to this thread, but FWIW, Jixee is a good alternative to Jira and Trello. A nice middle ground. (I am an employee).
We're great for teams that have outgrown Trello and teams that don't need everything Jira offers. We connect with Slack/Github/Bitbucket and more.
Sorry for trolling, just found this thread and a lot of the concerns expressed here are why our customers have switched to Jixee.