I don’t know how many times have I changed my preferred task manger app. For many many years it was Google Tasks. Why? It’s very quick, simple, and free. Though Google hasn’t discontinued Google Tasks I would say it’s obsolete.
It may be the preferred task manager of Matt Cutts but I’m pretty sure that Google Tasks will be among Google’s Spring cleaning list someday. Because they haven’t updated it for several years, there’s no mobile app, and they haven’t even updated its favicon (it’s ugly now).