When should I apply for a US visa instead of an US ESTA?

You can apply for a US visa instead of an US ESTA if:

• You want to enter the US on a non-signatory air carrier;
• You would like to remain within the US for longer than ninety days;
• Travelling to the US for any other reason apart from short-term business or tourism;
• You believe that any of the grounds of non-admissibility to this Immigration and Nationality Act apply to you.