I’ve changed because I write all of the GTD setup guides and it can help sometimes to fully immerse myself in the tool. Other times I’ve changed just because I want to try something new.
In my own experience of GTD I think I have " the award" of changing tools !
I selected a short list of tools which were Things, Nirvana and Omnifocus I used time to time :
I love Nirvana (100% GTD and so great but there is no real export/import to safe and import my datas) and Things (it's so beautiful and the mobile app in just so amazing) Sadly, these two tools are far away less powerful than Omnifocus...
Finally I stick with Omnifocus, this is why :
1. It tooks me a long learning curve to fully understand it, now, I know it by heart !!!
2. I can make every thing most of the others software are doing, thanks to the " perspectives "
3. I can show my items in two ways and see my data mainly like I want
4. As I invested all the time I found it was silly to use something else.
5. Omnifocus is imperfect but it works à 95% for GTD.
With Omnifocus I can make whatever I dream or want to do !
It is like a toolbox... So, OF is indeed a good software (PS I have no shares with omnigroup
)