I liked toodledo for the fact that you could email tasks to certain lists. I did not like the fact that I could not see an archive of my completed tasks. This was especially true for projects. I like to have the option of reviewing my accomplishments over the course of the year.
You can see completed tasks with toodledo, they don't show up by default on your lists but you can set up a search for them, just select 'checked off' as a search criteria and set it to 'yes.'
Completed tasks are kept for 6 months on the free account, 2 years on a Pro account and indefinitely on a Pro Plus account.