I used to be a Things user myself. My opinion is that (as soon as they get cloud sync sorted out) when your task management requires only one layer of tasks - separated by tags - per project, then Things will be the way to go as the user interface is very nice and the whole program has a "light" feel.

If you need more depth in taking control of your projects (work-related or personal) Omnifocus is the way to go. I personally find the userinterface in Omnifocus to be pretty good as well (in iPad, excellent!)