I ran a quick tap trial on some of the leading task managers available for iPhone. Following is a briefing:

To insert an undated task the number of taps required are:

RTM 4
All others 2

To insert a task for "today" the number of taps required are

Rtm. 5
To do 3
Things 3
Toodle 3

To insert a task with a specific date and a note the number of taps required are

Rtm 14
To do 8
Things 9
Toodle 6

It is obvious that RTM must definitely work on reducing the number of taps.

I returned to RTM even though I already own the other apps because there are advantages to RTM. One of them being the landscape mode in iPhone. The other one being that all new tasks automatically go to "Inbox" which is key in GTD.

I firmly believe RTM is the best app in its kind. I do not miss subtasks too much because I work with smartlists and also, I use the notes feature for that purpose.

It is important that the number of taps be reduced through a "quick access" like the one in Appigo's ToDo. I do not like Appigo's ToDo since their design is absolutely horrendous. It does not support subtasks either. Toodledo is great but their UI is also quite ugly. Neither one of those apps support landscape. Things is limited to Mac and, at $50 plus $10 for the iPhone app, it clearly follows Mac's example of overcharging.

Bottom line? I don't really mind no subtasks and I love landscape option but taps must be reduced.