Hello,
Well for once I will say I know something and its hard drives!! I do this for a living..and most hard drives of ok fine...I use many, and I mean many...I would go for the esata connection first if your pc or system has an esata port.
If not then firewire 800.
Drives can last a long time but there are always exceptions. I just had a reputeable 1.5 TB USB external die in 28 days of working and in the middle of a 100gb file copy...the heads crashed and made wonderful noise!!
Drives are relativly cheap.
I backup up gb's of data to several drives, internal and external. My insurance is one of these drives will survive. Having drives internal makes things easy to use but they give off a lot of heat.
You can get a really neat External adapter that you can plug in a sata drive connect to your system via usb or eSata. This way you can backup up to one or more physical drives and store them away and once a month plug them in to get the disk spinning etc....
Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153071I have 4 drives with the same data on all 4 and have them stored away. I plug them in once a month just to spin them up.
I also have my pc running RAID 5 (three drives) with the same data stripped across them.
Running an external drive is better than one main drive but a third is that much better.
Also before you buy, you may want to check the vendors website to see if they have any firmware updates, Seagate and others have had issues with the newer large sized drives with loosing data, drives that cant be accessed etc....
Food for thought...
All the best
Alex