What is the difference between Apex Data Loader and Import Wizard as far as displaying
error messages is concerned?

Answer: Apex Data Loader

Explanation:
Always gives error messages for failures. Error message given if text value provided in field
of type number and loading of the record fails irrespective of whether the field is a
compulsorily required field or not. Import Wizard. Is not consistent in giving error messages.
For example, if a text value is specified in a field of type number (PAN number custom field
created on Contact of type Number),