I have always been a user of the Franklin Planner and when I started using Smartphones I was using Plan Plus for Outlook in conjunction with Pocket Informant on a Windows Mobile phone, or a Franklin Planner program that at the time was part of Plan Plus.
When moving to iPhone when the iPhone 3G first came out there was very few programs available for task management. Appigo's ToDo was one of the first and I have been using it ever since. I now use the ToDo Cloud version which is the subscription based one. It does offer more features than the non subscription based one and overall is still a great program. The Mac version may look date but it still has the same functionality as it's iOS counterparts.
Over the years I have tried other task apps and each one has specific features that I like and therefore I now use three different apps, ToDo Cloud, OmniFocus, and Pocket Informant. Besides those 3 apps I also have tasks listed in BusyCal2 which syncs directly with Apple's own Reminders program. Each app has different features that I like and at this point just can't do without. Some may think that using so many different apps is a bit of overkill. Overall though ToDo Cloud always comes to the top of the list. Here are some of the top features of each app that I like
ToDo Cloud. Works great because you could set up tasks as checklists, or create a task to email or phone someone. You could set up a project with a list of tasks due on certain dates and those tasks could be set up as checklists or phone calls etc. With the ToDo Cloud syncing, syncing happens instantly across all of my devices. For the most part this is my go-to app for tasks. It was also my first introduction into the GTD methodology and although GTD is confusing at first once you start using it, can be quite easy and customizable.
OmniFocus.- This app is a powerhouse and I often go between this and ToDo as to which I prefer. This app has a higher learning curve than ToDo and their new OmniFocus 2 app for the iPhone is very nice. They are working on a new OmniFocus 2 for Mac, but there is no clear timeframe when that will be out. This app does not have the checklists feature like ToDO has, but it does have alternative ways to have them, which by the way could also be done with ToDo. Another great feature of OmniFocus is that it has perspective views and as a review feature where you can review all your projects, contexts and whatever on a regular basis so nothing falls through the cracks.
Pocket Informant. This app is available on iOS, not on Mac OSX. Of all the task apps available out there it is the only one that allows you to use the Franklin Covey method rather than GTD. Having used Franklin planners for years and attending and facilitating their seminars for years I am very well versed in their methodology. So this is the main reason I love this program. For those of you that are GTD users the app can be configured for that as well. It also is integrated with calendars notes and is pretty much the equivalent of having a daily planner with you.
As far as Busy Cal 2 goes, I like to use it for my calendar on my Mac over the Apple built in calendar, although it does sync flawlessly with the Apple Calendar so that works well with my iOS Calendar. As for the tasks the task list is good and basic, but one feature it lacks the most is that you can't have start date for a task. All the other tasks apps I use have this. Another feature, and downfall, is that it syncs with Apple's Reminders app. That inane of itself is good, but when you use reminders to check off a repeating task on iOS, it does not carry the repeat, it changes the task into a one time task and that's it. So I rarely use iOS to mark those tasks as complete.