So what do you suggest?
If you are looking for speed, get 2x1TB and RAID0, if you are looking for fault tolerance, then 2x2TB in RAID1 (mirroring) this way if one drive fails, the second drive in the array will be accessible. However some systems will format all data once the failed drive has been replaced, so in essence you should still have a backup to any array regardless.
The misconception that people have is that having a RAID system is for backup purposes but it is not.
RAID is short for redundant array of independent (or inexpensive) disks.It is a category of disk drives that employ two or more drives in combination for fault tolerance and performance.
A good practice is to have a backup to a RAID system.
I have 2x1TB drives as RAID0 within a RAID enclosure, but all the data on the RAID0 is backed up to 2 external 2TB drives, that is how much my data is of value to me.
Hope this helps.