SATAII Raid. redundancy worth it?

[Quantum Flux]

I will be building a new pc soon. i decided on sataII raid. i dont know yet if i will use raid 0 (with 2 drives) or raid 0+1 (with 4 drives). How reliable is striping? is it worth the extra cost to get redundancy and also is there any speed improvement with redundancy?

thanks.
adam, australia.