This is the absolute truth from my point of view - over the years I've seen dozens upon dozens of failed hard drives. Some die in less than a year, some were 6+ years old. Typical age is 4-5 years. I've come to a personal conclusion that brand, model, capacity, PATA, SATA doesn't matter. Any drive can die at any time for a variety of reasons.
Hard drives are a commodity item these days and typical cost between a 160GB drive and 1TB drive is maybe $50 (if that much). What I look for in a drive is capacity (in your case, no more than 500GB) and rotational speed. Warranties mean nothing to me. I mean, if a hard drive fails what am I going to do, send it in with all the data on it for a refurb in return? Nope, I'm destroying the drive and buying a new one. That's just me, the paranoid guy that I am.
Bottom line, you're looking to save money, go with the less expensive, unless the rpm & cache is lower. I'll spend a few extra bucks for better performance. However, I never like to think that one particular drive is going to outlast another. That being said, make sure there are good backup proceedures in place