Thanks to vereyone for their answers so far. Really helpful..
A couple of things I’ve come across….
Many of the offline apps use Gears (RTM in particular). Gears have never worked consistently for me – even with the Chrome browser. I’m afraid I’m a Firefox person so I need offline that isn’t Gears based.
The RTM web interface doesn’t work for me and the fact that the google gadget redirects to the website to add notes isn’t good (but still – RTM is one of the best….).
I like Toodledo for it’s goals and contexts and so on – RTM doesn’t come close to this but the lack of offline is a problem.
Todoist is simple. But too simple for me (but I do like te task hierarchy – it’s neat).
I guess I’ve just gone back round in circles again…......