I know there's a ton of todo apps out there, I've tried Remember the Milk, Evernote, Wunderlist, Reminders.app, and probably a couple other iOS todo apps.

I picked Wunderlist and have used that for a long time because it's on every platform I care about (iPhone, iPad, and Mac) BUT it's absolutely horrible about syncing content and I get duplicates and missing todos all the time. I just tried out cheddar's "push" feature and it's actually enough for me to leave Wunderlist.

Also the Markdown feature is awesome