I think the choice of a software is personal. I wrote a lot here explaining the differences i found about Things, Nirvana and Omnifocus.
The more I practice GTD the more I realize that the simplest system suiting to each people need is the best system. There are no best software, nor best systems. I think we could build a good GTD system with simple . txt file or sheets of papers. No doubt it could be as efficient as my system is for now.
Anyway when things becomes professional it's another game to play. Each mistake is paid cash and believe me it may be expensive ;-).
I paid a lot for learning that. Also, security, archives, searches becomes crucial.
As I often said I don't have any shares with Omnigroup. I often Find Omnifocus complex and sometime cumbersome. Sometime I love it. Sometime I hate it. However it is the best software I ever used for a long time. It can manage securely a tons of datas and well made it is just an astonish software. Of course like many things it takes time to be fully efficient
it is a fantastic tool I can trust.
If only things could be as powerful as Omnifocus I would choose Things. Sadly it is not (like Nirvana). It does the job but is to light for me.
Omnifocus is like a lego. It is an open choice. The danger is to dive too deeply inside it and forget his main purpose : eg doing things.,
Happily, I passed this step. Now I work with it efficiently and made it indeed powerful and efficient as I dreamt. It was quite a surprise. Sincerely I thought It would never happen.
Nothing is perfect. As I work a lot with .txt file I often think I could use obsidian or simply .txt file into folders.
However when I search things (what happens frequently) Omnifocus make it fast and easy.
Omnifocus became little by little a good companion.