Best for low cost redundancy but worst for performance. If your looking to improve performance, use RAID 0. This provides no redundancy as the failure of any one of the drives will result in loss of data. RAID 1 will allow for redundancy with only a slight performance hit on writing as the data needs to be written to both drives to provide redundancy.
RAID 5 provides good performance on data that is rarely updated but it sucks for writing as it needs to read and write the full stripe plus the parity even if you are only updating a small portion of the data. Depending on what database engine you are running and what you are using the data for the performance hit could be worse than running on separate drives.
RAID arrays will only protect you against loss of data in the event of a disk failure but won't protect you against data loss from accidentally deleted files or a poorly written update query. You still need to back it up every day.