The case have more in common than not. Some of the aluminum ones are designed to cool without a fan, but if you're not running the drive more than short periods cooling isn't an issue. If the drive will be on all the time, get a case with a fan, or go with a 5.25" case which will have a fan. A 5.25" case also has the benefit of being compatable with burners, and has enough air space in it for a HD to really stay cool.
Apart from that, the main consideration is firewire or USB2, or both. Dual-link cases are more expensive. Firewire has much higher throughput on sustained transfers than USB, and tends to be less troublesome.
As to chipsets, I believe the Prolific chipset has been more reliable than the Oxford.