Please ignore mwryder55's remarks. Optical media generally degrades at a much faster rate than hard drives do. The misconception that optical media lasts much longer was only based on early advertising when optical was much more expensive, and manufactured to much higher standards. The crappy optical media sold in stores today will degrade in just a few years unless kept in absolute darkness and away from any source of warmth the entire time.
Besides, burning that many CD's would take a lifetime, and you'd be constantly burning out the burners.
Hard drives can safely store data for decades without issue. Even if there is some minor degradation of the magnetically stored data, each sector contains ECC code which is used to repair the damage. Video files are also pretty resilient to a small amount of corruption. A few lost sectors is unlikely to make a file unplayable. It just might have a few glitches in a couple frames if that happens.
As to reliable hard drives, most drives in the 160Gb size are pretty reliable. I'd probably avoid WD if you're planning on long term storage since those are prone to firmware glitches if they develop any bad sectors (which they might if sitting for 20 years). Seagate drives weren't too back back then, it's their newer drives you've got to watch out for.
However, if you're actually considering your price per Gb cost, it might be a more effective solution to buy 2Tb drives. Especially if you get HGST brand 2Tb drives, they will hold up really well for you. At the current pricing, it might be an easier solution to do a mirror set of 2Tb drives so you have a second copy of everything.
Unless of course you've got a supply of 160Gb drives available that aren't costing you anything.