Best Task Mgr: Depends
I have used G-Tasks for a while, and it does a great job. Integrates with Google Calendar Tasks 100% and the developer is great. I have used Astrid but the sync feature in GTasks makes it win for me.
I have moved to GQueues. Not a native client, but it allows me to share/delegate lists to my team members. This positive is 100% offsets not having a dedicated client. I can have lists for my maintenance men, supervisors, and store managers and we can add tasks to each others lists, and I can oversee these lists.
A more family example would be shopping lists, home tasks. My wife can add to my list to fix something, or that she needs something from the grocery store. If I have time before coming home I can pull up that list and get what we need from the store. GQueues is newer but if it continues like it has it has HUGE potential.