I've never used a RAID, though I'm planning to for my next PC, so I've been researching it a little.
So far RAID5 is my favorite RAID, though, I don't know if I'd do it unless I had four hard drives or more. RAID5 doesn't have as high of a performance increase as RAID0 (some argue that even RAID0 doesn't even increase performance that much, I'm not sure), however, RAID5 is said to be pretty close to that of RAID0.
However, you should always try and backup critical data if you can. Though it is unlikely that two drives could fail at the exact same time, it's not unheard of. Especially if you buy all your hard drives at once, they'll be from the same 'batch' of hard drives, and likely contain similar defects - increasing the chance that multiple drives fail at the same time, or for the same reason.
Even with this in mind, I think the protection from a RAID5 would be enough that I'd sleep better at night.