I’ve tried them all, and Things is the one for me.

I used OmniFocus for a couple of months. I really wanted to like it, but despite having a great company behind it, it's rigid, unintuitive, and unattractive.

iGTD’s UI is an utter mess, and Midnight Inbox is extremely buggy.

I think Things is poised to become the new “it” GTD app. I've been using it for a couple of weeks, now. It allows for structure, while simultaneously allowing for flexibility. It doesn't force either upon you (which unfortunately is not the case with OmniFocus).

Things is gorgeous, intuitive, and deceptively simple. It’s not even in beta, yet, and I’m already sold. They've been candid about their immediate plans for it, and I'm satisfied. I migrated everything out of OmniFocus and into Things.

(Disclaimer: I’m not affiliated with Cultured Code in any way. I’ll be paying for Things, like everyone else.)

Also, I don't dislike Omni -- not at all. They're good folks who make great software, but OmniFocus simply doesn't meet my needs.) I gave it the old, college try, but its approach is too rigid for me and has too many “rules.” OmniFocus felt like a babysitter; it's her way, or not at all.... Then I found Things: Gentle structure, but equally flexible. The Cultured Code guys really "get it." To me, Things is “GTD for grownups.”

OmniForgotten.