Really depends on your requirement , for non critical VMs I'd use RAID 5 , for critical VMs I'd use RAID 10 . AS RAID 10 uses more disk just be aware of the number of disks required . In both the scenarios use on spare disk .
If you have some backup solution, then I recommend use 1 to 1 mirroring on esx install disk and then use RAID 5 with one spare disk for your VMs storage.
Hope this helps