Try Intention+ally for GTD
I tried OmniFocus as soon as it came out (years ago) and found it to be way too unintuitive. I admire OmniGroup for having the first app that truly adhere's to David Allen's methodology on the iPhone, however, Apple hadn't fully developed their UIKit and CoreData frameworks at that time. As a result, OmniGroup had to settle for an unintuitive user interface and a data model that is not fully supported by Apple.
So I decided to make my own -- I call it "Intention+ally". It does GTD without hogging space on your device or trying to be something it's not:
* Its user interface is intuitive! (for example, tap & hold on any Action to convert it to a Sub-Project).
* It integrates your on board Calendar and Contacts apps (the ones that come with the phone) into your Actions. These sync with their desktop counterparts on your Mac.
* Uses Twitter-style hash-tags to permit you to fine-grain your contexts into as many sub-contexts as you like.
* Search: Scroll to the far left and enter search terms or tags into the Search box. For example, enter "#internet" to reveal all tasks with the #internet context; enter "#internet #home" to refine that search to those items that should be done at home).
* Intention+ally is free to try and buying it costs half as much as the OmniFocus app!
If you live on your phone, then I think my app wins vs. OmniFocus; Intention+ally's database syncs to your Mac via your iTunes sync. However, if you prefer to do your weekly update on your desktop and you can tollerate OmniFocus's user interface, OmniFocus wins (for now!). I am developing a web interface for Intention+ally that is waiting on the release of Apple's upcoming iCloud service (I'm excited about this!).
Check out the Support page and Forums for OmniFocus:
http://www.omnigroup.com/products/omnifocus_for_iphone/support/
http://forums.omnigroup.com/forumdisplay.php?f=49
Incidentally, I work hard to avoid needing a support page. It's the 21st century; apps should be self-sufficient and intuitive!
Intention+ally is here:
http://goo.gl/w2Jos
Again, I am the developer of Intention+ally and I am at your service.