I only use Appigo Todo on the iPhone. I don't need start dates nor do I use filtering or sorting. For me, I prefer the way they display parent task/subtasks (single tap to see all subtasks), and I find everything generally takes a single tap rather than having to go down an extra screen level or have to scroll to the bottom to access notes, etc.
And I find the look and feel intuitive and appealing, whereas Toodledo looks and behaves kinda like an older generation iPhone app. Very functional, but just not making the most of iOS. Mind you, the Toodledo website is a bit sad looking too so I guess it runs in the family.