Call me cheap but I’m not a kind of guy to pay for a to-do app. There are at least a dozen of good free options. My favorite is Wunderlist. I used to like Todoist a lot but it has a lot of locked features, especially when it comes to syncing with other apps. Wunderlist is much better on this account. I just started using it but I already love it. I like its design more than Todoist but as I already mentioned, it’s also much easier to sync with calendar and other apps.