The Import Wizard
is designed for less-technical users and smaller, simple imports of up to 50,000 records. It takes you through the process step by step and displays error messages to alert you to potential record duplications (“dupes”). For more information, go to Help & Training | Importing Data | Using the Import Wizards.
Use the Apex Data Loader
for complex imports of any size. It’s for technical users only. You’ll need access to the API to use this tool, which is included with Enterprise and Unlimited Edition. If you have another edition, you can purchase the API separately by contacting your account executive. The Data Loader doesn’t display error messages to alert you to potential problems. However, this tool includes several features that help make large data imports easier, such as being able to save your mappings. For more information, go to Help & Training | Data Loader.