Thank you for your comment and my apologies for the late reply.
Well, at the time when I got 2Do the Toodledo iPhone app didn’t have certain features that 2Do had. For example, it wasn’t possible to order folders manually or sync them in the same order as on the Toodledo website, which made GTD impossible. Also, an appealing UI is important to me because otherwise I avoid looking at my to-dos and therefore don’t get things done. I chose 2Do because I preferred the UI, in addition to it offering functions that Toodledo didn’t. It may have caught up since then.