Import Wizard:
For simple imports of up to 50000 records.It supports all custom objects and only few standard objects like Account, Contact, Leads, Solution.It supports schedule export.Delete operation is not available.It doesn’t require installation.While importing, duplicates can be ignored.Data Loader:
For complex imports of any size more than 50000 records.It supports all standard and custom objects.It doesn’t support schedule export.Delete operation is available.It requires installation.While importing, duplicates cannot be ignored.