> It is frequently asserted that users prefer chatbots

Who is asserting that? Is there data to back it up? And which audiences are we talking about? Which products? Which industries?

As far as how I'd decide, I'd ask people. Data is a good thing to use when making decisions. Don't let data dictate all decisions, but don't just blindly guess either.

Personally I hate chatbots and natural language interfaces. Give me a well-structured window with widgets or better still a command line. Case in point: that now when you double click on a time in Apple’s iCal it brings up a free-entry text box to “describe” the engagement rather than a structured window with title, location, beginning and ending times drives me insane.

Would be interesting. Personally also hate chatbots. If voice would be integrated to the gui with instant reactions it would be cool. But currently these things are to slow. Chatbots depend on what you doing with it. search a document in your paperless? probably better then doing it yourself.

Gui and chat/voice needs to merge with fast gui feedback.

Depends on the product.