Probably the website since it's more useful for the task. Plus apps aren't cool or physical (unless you mean the touching your phone part). I could see the word-of-mouth factor being higher for an app, but the app would have to work very well for the task and I don't think that's something that would be easy to achieve with the form factor and the fact that most devices deny you a physical keyboard. So maybe something that only requires light editing and pulls most of the data from outside sources?
I see your technical point of view, but the average user market shows something else. People couldn't imagine doing stuff they do on a phone before iPhone. Now they do all sorts of mass content creation and they prefer it.
UI is just a matter of how much energy you put into it. It's not easy, but can be done. See iMovie, mobile bitmap editors, Garage Band... Difficult and unbelievable 5 years ago, but clearly doable.
