I'm not an expert in GTD and associated tools. After reading the D Allen books and some research on the web I picked up things for iPhone and iPad. Using it for a few months the lack of structure in the project list (can become a long list to scroll through) made me look for something else. I then took OF (OS X, ipad, iphone) and saw a lot of use ins possibilities to tweak, structure projects and actions and the built in weekly review. After using that for some time I noticed I still used for logging actions, but most of the time fixing thes on a date, the complexities (probably my OF setup) made me look at my actions less frequently. So this week I returned to the simplicity of things. The daily review process brings more actions to my attention every morning. The tags can provide structure (still tweaking that). It just seems to be easier to use and gets used more and better for that.
One disadvantage for both is that the two of them are keeping me locked in Apples garden (while the android grass seems to become greener)