Yeah it's a great app. I've had it for a while now. The only caveat to it going free is that I believe that there are some features that are IAP still. This is their announcement today on why it is free. http://www.2doapp.com/unchartered-waters/
I've tried a few and have settled on 2Do.
Among other things:
Nice UI, including drag & drop
Can sync with computer, Toodledo or MobileMe
Can view tasks based on location
I had the same problem, it took me weeks to find the right to-do app.
I now use 2Do and it's the best I ever tried. Lacks a web app but that's hopefully going to change in the future (and tbh I'm using it just fine with the smartphone).
I haven't explored if the app has calendar integration or not, but if you use pure GTD that shouldn't be a problem (inbox/task management and calendar are to be used as two distinct systems).
Give it a shot, if the other apps aren't your thing this one probably will be.
Perhaps using a sync method other than Dropbox would help? Reminders seems to have some kind of CalDAV support, but I haven't tried it... http://www.2doapp.com/kb/article/which-sync-method-should-i-use.html
It does matter if your variable has spaces - and you can use URL Encoding to overcome this.
You need to use an X-Callback URL to bring you back to workflow after adding each task - I'm not familiar with 2Do but there is documentation for it :)
And 50% off for OS X. It is, by far, the best productivity app/suite I've ever used. Free for the next 7 days.
Their website: http://www.2doapp.com/
For future reference and for people that might be in the same situation, I ended up using 2Do. I like how much you can customise all the various aspects of a task, and I love the interface.
Now enough with the preparation, this weekend I'll take my time to start actually implementing the system
If you don't mind paying $8 for the iOS app and $25 for the Mac version (pricing @ 50% off the regular price), 2Do sounds like the the app you're looking for. And to make sure it's the right app, you can down a 21 day trial version for the Mac here (although I'm not sure how long the sale is on for):
I have not personally delved into this app but it got high praise. Might want to take a look. I got it for free at one point so I'm not sure if they have a price on it again.
One App I use regularly although it does work out quite expensive to have running on both platforms is 2Do as a task manager. Syncs brilliantly between my android phone and all of apple devices ! http://www.2doapp.com The android app is pretty ugly mind !
Try 2Do. It's right now only available on iPhone and iPad, but it syncs with reminders and is a lot faster to make a reminder a lot quicker.
Bad news though: it's expensive-ish. $10. Worth it for me, but because there isn't a good mac app yet (you have to use the Reminders app, which doesn't have as much functionality as 2Do) and it doesn't sync with anything for PC that I know of (I haven't checked recently), it might not be the best for you.