If I had to suggest a task management service from the ever growing list out there it would definitely be Wunderlist hands down.
This has been my personal favourite because of how I can keep everything synced across all my devices and it is completely free.
The three main devices I use on an daily basis are my windows pc, my Android device and my iPad. Being able to manage my tasks across all three platforms quickly and then having them sync across is simply brilliant. There is also a web version so you can do everything within a web browser.
This is the Android version of the app and as you can see a very clean look and to the point. It also has a notification system so you can notify yourself when a task needs to be done. You can even customize the app, for example you have change the background.
This is the browser version of the service. Very clean and everything can be accessed and changed from here.
This is the iPad version. Again very clean and minimal. The iPad version also supports push notifications so you don't miss a task.
I definitely recommend it over any other task management service.