What tool should an architect recommend for migrating approximately 10 million contact records into Salesforce?

The recommended tool for migrating approximately 10 million contact records into Salesforce is the Salesforce Data Loader. This tool is specifically designed for bulk data operations, making it highly suitable for large-scale data migrations.

Data Loader excels at handling large datasets, with the capability to process up to 5 million records in a single batch job, and it can run in both user interface and command line modes, allowing for automation and scheduling of data loads. Moreover, it supports both inserting and updating records, which is essential for a comprehensive migration scenario.

While other tools, like the Data Import Wizard, can handle data imports, they are typically more suited for smaller sets of data, typically under 50,000 records, and often lack the advanced features needed for large migrations. The Excel connector is aimed at simpler interactions with small datasets and isn't built for extensive data migrations. Salesforce Workbench, although useful for various metadata and data operations, does not focus on bulk data loads in the same systematic way as the Data Loader.

Considering these factors, the Data Loader stands out as the most effective tool for efficiently and comfortably transferring a significant volume of records into Salesforce.