I am committing using Wunderlist to manage all my non-day-job to-dos. I paid for a Pro subscription so I could take advantage of all it’s features.
The reason I selected it (besides the reviews of friends) is the iOS, Android, Mac, Windows, and web clients. [There’s a Kindle client too...] I work on a variety of machines and enjoy having access in various spaces. Plus, having a client that is accessible (and robust) on a full computer allows me to quickly add, remove, and edit.
Every to-do item has, if possible, a due date so I don’t loose track of it.
Since Wunderlist doesn't have geo-fencing, I use iOS reminders to suppliment. The geo-fencing reminder I use the most is for regular doctor visits. I’ll note stuff I want to ask her about. For example, I really want an allergy test. I set it to remind me whenever I get to her office’s address.
Wunderlist is free http://appshopper.com/productivity/wunderlist-task-manager. There is also a “pro” service that one can subscribe to, but it’s not necessary.