Coincidentally, not long since I read a chapter on the shape of axe handles in The Ax Book: The Lore and Science of the Woodcutter by D.Cook in which the author makes a convincing argument for the straight handle being preferable to the almost universally adopted s shape. The main reason being that the straight handle delivered the axe head more precisely with the s shape magnifying any inaccuracies in swing. I haven't got the book in front of me at the mo but there are even mathematical calculations provided to back up the theory!
The piece goes on to point out that the s shape appeared some time after the axe had been largely replaced for serious commercial felling by the large felling saws and eventually the chainsaw. Prior to that the most popular pattern in commercial felling had been the double bit axe - with the straight handle.
It's an interesting theory that the s shape handle with its perception of delivering more power per swing and fashionable appeal might have been short lived, being perhaps tried and subsequently disgarded by professional lumberjacks had the axe itself stayed longer as the primary felling tool.
My axemanship isn't of a sufficiently high standard to judge
.
The book is a great read though.