How about Appigo Todo? I think we may have discussed this before on the forums but I can't remember if you've tried it out. There are versions for iPhone, iPad, Mac and web-browser.
Originally Posted by mcogilvie
In my view the iPhone & iPad versions are fantastic, simple yet powerful and well designed. The Mac and web-browser versions share a similar looking UI which is functional although I feel could do with some improvement, and I understand Appigo are working on this at the moment.
I can vouch that the system syncs reliably and fast, and support at Appigo is good.
I checked out the latest Toodledo iOS versions recently - definite improvements there although the website hasn't changed and I still have niggling issues such as lack of an inbox, inability to manually sort, etc.