I use Things for task management with DEVONthink all the time and it works great. Using the Things clipper keyboard shortcut while something in DT is selected and you get a task with the unique DT item link in the notes field. Same with emails in Apple Mail. Then manage your tasks or projects in Things and use the links to quickly link back to the exact item in DT or email message in Mail. Fantastic thing about this is that those links work for DT and Mail on both the Mac AND iOS!
But to the orginal question, I also use other apps but consider DT my permanent archive. I will store relevant current documents in it with links like I described above to reference them. But sometimes other apps are better for specific tasks, like Ulysses which I also use, and also has good linking ability. I find keeping active updated notes in DT doesn’t work so well as the cross-platform syncing (Mac > iOS) is not as fast and seamless as with something like Apple Notes. So, I will use Notes for very active things and then archive it in DT when things settle down.
