If you need straight up speed, then RAID 0 as it is cheap and offers very fast speeds especially if you short stroke. The reason to use this is again speed and disk space for cheap. Problem is if one drives fails you loose all your data.
RAID 1 is mirroring, meaning you have exact copies of your data across 2 drives. Great for data security but it is slow.
RAID0+1 - This gives you the benefit of RAID0 plus RAID0 - mirroring and striping. This allows you to have speed along with data security. Problem is it isn't the most expandable
RAID5 - Offers the best in terms of data security but is slow when it comes to writing data, and isn't nearly as fast as reading as RAID0, but you have to be willing to sacrifice for data security.
You need at least 3 drives. But if one fails you don't loose any data PERIOD and there is no down time. Just take the dead drive out, slap ina new one and the system rebuilds. Problem is if you loose more than 1 drive your boned. Problem is that you "loose" a disk to parity.
RAID6 - rare in the civilian sector - offers the advantages of raid5 but is more resilient allowing up to 2 drives to fail
Although personally you don't need a RAID controller as your onboard will work just fine.