After trying dozens of personal productivity tools for web/mobile/desktop (and writing my own Asana clone[1]), about 2 years ago I settled on Trello. I use it every single day, many times a day. I find it's the perfect balance of flexibility and simplicity for me. Plus it's free.

Having said that, when I've tried using Trello with teams, I tend not to like it nearly as much.

I think the Hard Problem with team productivity tools is optimizing for both individual organization and organizing individuals. I've never found a tool that's good enough at both for me to be fully satisfied.

[1] https://github.com/aroman/keeba http://keeba.jbha.org/about