The more vdevs in a pool, the better the overall performance.
IOW, one mirror vdev will be ok. Two mirror vdevs will be faster. And three mirror vdevs will be even faster still.
Regardless of the RAID technology used (software, hardware, zfs, etc), you want your individual RAID arrays to be made up with the fewest drives possible. And you want to add as many arrays as possible to the system, striped together (RAID60, RAID50, RAID10, etc).