As far as I'm concerned they are all much of a muchness - if you take them apart they often have the same hard disk inside them, as there aren't that many manufacturers of the actual disks! I have both Lacie and Western Digital units, very happy with both.
As said by others, if you're doing video and/or photos, main thing is buy one that's big enough as it fills up very quickly!
And make sure it definitely is a portable USB one, not a desktop USB one, as the latter normally need an additional power supply.
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