The best hard drive to use for RAID will depend on your specific needs. Generally, SATA drives are reliable and cost-effective for most scenarios, although SAS drives are often used for applications that require higher performance. When considering RAID, it is important to choose drives that are designed for RAID and have the same specifications, such as spindle speed and capacity. Additionally, some drives are optimized for RAID, so it is important to research the specific drive to ensure it is suitable for your needs.