Having at one time or another used external drives from all manufacturers I have yet to find a "best buy".
It usually comes down to which seller has the best deal on whatever manufacturers drive at the time of wanting to make a purchase.
What factors? Would a network capability be useful on the drive - this will of course raise the price. click here
Do you require a portable drive or is it to reside permanently in one place. If portable then one without a power supply click here, if fixed then a powered one might be better.click here
All links are for example only and not a recommendation.