I have a slight preference for the current layout, but it may just be familiarity. I don't hate the demo site layout, and I could likely get used to it. I think my preference is because we're using mailpiler mostly for searches that touch on multiple recipients mailboxes, and I like having columns for "to" and "from" directly visible in the search results.

My problem with the demo site layout is that it requires at least 3 lines for each mail in the list. When I use the archive, I usually have to search for a specific mail in a long list of candidates. In the current layout you get one line ( with long subjects two or more lines) per mail, making better use of the space on the screen.
Just like @thatgeek I also prefer the dedicated columns in the current layout.

It would be great if the width of the columns could be adjusted with the mouse and oversized cell contents are clipped (e.g. using CSS text-overflow: ellipsis ellipsis;) so that each mail is strictly printed in one line.

BR,
Frank