It's all about building report with users: make them feel like your web app is an actual person, and they tend to trust you and want to use you more. What's be

It's all about building report with users: make them feel like your web app is an actual person, and they tend to trust you and want to use you more. What's better: a cold, formal tone that is very professional, or one that is casual and makes you feel like an actual person is behind the monitor? It's all a matter of opinion, and definitely depends on what you are selling. Banks? Definitely shouldn't be doing that.