I would like to like Omnifocus, but I have found that I just won't use it. It seems to me to have a lot of infelicities: Navigation is painful.
Keyboard shortcuts seem terrible: control-command-right arrow to indent? It's hard to get data into it (but somewhat easier to get it out). It's not any one thing I can point to, but it seems unpleasant, almost un-Mac-like to use. Just not simple and fast for me. I love Omnigraffle, and like Omnioutliner, but I would recommend giving Omnifocus a full trial before buying.
I am using Toodledo, a web app, and can recommend the Remember the Milk, another web app, as well. They are fast and simple to use, but both have considerable customizability. Both are cheaper than Vitalist. Because I have an iPhone, what I do may change in July when the iPhone app store opens for business, but may not.