Hi,
The difference is in the features basically and the purpose for which the component will be used. smart-input is perfect for small amount of data while the dropdownlist can be loaded with thousands of items in the data source. Things like popup resize, checkbox selection, radio button selection and many others are available in dropdownlist and not in smart-input. Basically, it depends on your needs.
Best regards,
Peter Stoev
Smart UI Team
https://www.htmlelements.com/