I have been using Things for a long time, both on my Mac and iPhone. While being very good at what it does and being visually beautiful, I have lately been having lots of trouble finding a good solution for a “Waiting For” focus, planner, setting a starting date, subtasks and other minor things. Their support forum is full of these requests and many other too.
Both The Hit List and Omnifocus do not suffer from these shortcomings, and have other benefits too. THL has a very nice planner where you can see items due today, the next days, next week, month etc. It makes it very easy to get an overview on what and when things have to be done.
The one thing missing in THL at the moment is iPhone sync, which is where Omnifocus shines! It has a very competent syncing framework and a native iPhone client (a bit pricey though). Omnifocus follows the principles of Getting Things Done almost to the letter, which may be too rigid at times, and it does not have support for tags at the moment.
What to do? I have invested in Things for the Mac and for the iPhone, but I have considered the idea of moving to Omnifocus for the moment, and maybe returning to Things when it has matured somewhat. I like THL quite a lot, but without syncing with an iPhone application, it’s useless for me.