What subscriber solution should be recommended for a business unit with high-frequency sends and large data imports?

The best solution for a business unit experiencing high-frequency sends and managing large data imports is to utilize data extensions. Data extensions are designed to handle large volumes of data efficiently and support complex data relationships, making them ideal for scenarios where frequent communication is necessary.

Data extensions are more flexible than subscriber lists, allowing for customization based on various attributes and enabling advanced segmentation. This flexibility is crucial in high-volume environments where specific targeting can significantly impact engagement rates. Additionally, data extensions can accommodate more data fields than subscriber lists, which is essential when importing substantial datasets.

In environments with frequent sends, the performance and scalability of data extensions also play a significant role. Their architecture is optimized for handling frequent and large-scale queries, ensuring that email delivery remains timely and effective. Hence, for the specific needs outlined in the question, data extensions are the most suitable and efficient choice.