I am mostly using Todoist for client work and todos. It's simple, clean got cool features with filters, labels, projects etc. And there are several integrations.
However I recently discovered rindle wich is pretty cool. I am trying out the beta right now.
It's a kanban board like trello, but the cool thing it's like a aggregator for your information. You can make so called "drops". Which are integetrations, for example if you get an E-Mail with a specific label it gets send to the board. It works also with jira, todoist, slack, basecamp, github, wunderlist etc. So you can keep things in one place. And you can make "Automatisations", which are rules that trigger events. Like if you put the card into the "done" list, it automatically completes the task in wunderlist or something.