*UPDATE* since writing the review below several months ago I tried a few more task apps and STILL find myself most happy with gTasks. My thoughts below are unchanged...
I never took Googles tasks feature in gCalendar seriously, yet wished I could. Perfect spot for a task list - right next to your calendar. But even Google seemed to ignore its potential. In a perpetual quest for a perfectly balanced Task app Ive been through many and often run two at a time just to see which is closer to my ideal. But after only a week with gTasks HD Pro Im so impressed with it Ive started moving my other task lists into it and stashing-away (or deleting) the other apps.
Clean, smart design, intuitive, fast syncing, allows nested task lists inside a task. And since Im also a google apps user it also lets me sync lists from multiple accounts. Google must be impressed - and a bit envious (maybe enough to acqui-hire?)
MyDenouement about gTasks Pro for Google Tasks, v4.8.4