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Probably number 3.
You have to remember that a huge percentage of buyers will only see the image briefly in ICON form as they look around, and so your cover has to sell the idea of clicking on it even before they see the large version.
Cover 2 is nice, but in a postage stamp sized icon it means nothing.
The best covers look great in small icon form, and then also have more detail revealed for even more wonderment in the larger form.
They also instantly portray the genre without the reader having to even think about it.
And mostly... nobody really knows how to measure the performance of covers without trying them.