The ETL process for SQL Server involves several stages, including extraction, transformation, and loading. These stages are critical to data management as they ensure data integration, quality, efficiency, business intelligence, data migration, compliance, and security. The top features to look for in an ETL tool include connectivity to various data sources, robust data transformation capabilities, scalability, performance optimization, data quality and validation, automation and scheduling, monitoring and logging, security, metadata management, version control, flexibility, and cost efficiency. Popular ETL tools for SQL Server include Microsoft SQL Server Integration Services (SSIS), CData Sync, Talend, Informatica PowerCenter, Apache NiFi, Microsoft Azure Data Factory, Apache Spark, and Pentaho Data Integration (Kettle). Each of these tools offers unique features and benefits that cater to specific business needs and data integration requirements.