Depends what you will use it for but generally RAID10 is a good choice.. safer and faster than raid5 although costs a bit more.
We used to use raid5 on a fileserver with a fairly big array (nearly 5TB in 24 disks) but performance sucked and when so many disks are involved things can and do go wrong. We switched to raid10 and its all so much better.. server loads are down, traffic is up and data is safer.. everyone is happy.