I'm migrating from Things to Toodledo for task-tracking, in order to satisfy a couple of new (to me) use cases that I can't handle with Things, but that it appears Toodledo will allow me to handle.
I have more than 3500 completed tasks in Things though, and I treasure my ability to search through the completed tasks to turn up info used for new tasks. It isn't acceptable to me to lose that data in the transition, but I don't want to have multiple task apps, so I want to migrate all of my data from Things to Toodledo.
Things supports certain things Toodledo doesn't, so the first thing you have to do is alter your Things data so it's in a style Toodledo can accept, and that may be imported well.
First thing is that Toodledo doesn't really support Projects. It supports "Goals" but to tell you the truth, migrating that data isn't easy, and I didn't attempt it. I simply made my Projects into Areas on Things, and moved the tasks in Things to those Contexts.
Toodledo also doesn't support delegation the same way Things does. In order to migrate your delegates, the best way I could think of to map it was to have a "Delegated" Context, and then take the Things delegate's name and tag the thing with it. That way you can search for specific delegates on Toodledo post-migration, and you'll know something is delegated, at least.
On Toodledo, you'll need to create Folders for each Area from Things, along with the "Logged" and "Delegated" contexts.
The second thing is that Toodledo doesn't allow you to import completed tasks. This is troublesome for me because I want that history. I settled on putting all my completed tasks in a "Logged" context so at least I could get them in Toodledo, then mark them all completed later.
Finally, Things URL format in notes needs massaging in order to generate clickable links on the toodledo site, and I implemented some logic to do so.
That's about it - if you run this Applescript from within Things, once for the "Next", "Someday" and "Logbook" lists, uploading to the toodledo site each time, you'll have all your data in there.
Then you just need to mark the things in the "Logged" Context as completed, and you've finished your migration. I used TaskSurfer to do that since the interface was so fast for completion-marking.