As I shop for a new espresso tamper, I see that there are a dizzying array of options for the shape of the base (i.e., the shape of the part that contacts the grounds) -- see some examples at Reg Barber. (I'm also aware that there are many shapes and sizes of the handle, and differing sizes for the base; I'm not asking about those.)

In part spurred by this recent question on the essentials of tamping, and other questions tagged tamping (which are mostly about pressure), I got to thinking that the shape of the tamper could have a significant impact on the result.

There also seems to be a fairly large amount of personal preference or opinion in this realm. I can't find any proper comparisons or trials; at best I can find conversations about various preferences (e.g., home-barista including this poll, coffeegeek, coffee forums, barista exchange). A few patterns emerge:

• curved bottom provides a greater margin of error for avoiding the "donut" effect of water channeling around the perimeter of the portafilter;
• curved bottom could over-compact the center;
• ripple shape is pretty, is used by some pros including winner of a competition in 2009, but has no demonstrable benefit, and is marginally harder to clean.

I hope I'm not spurring a sectarian flame-war by asking this; so I try to ask as objectively as possible:
Is there any objective benefit for one tamper base shape over another?

For example, side-by-side trials; experienced use beyond preferences; ...