My all-time favorite handlebar shape is the old AVA Randonneur:
The Randonneur shape makes the “behind the hoods” position even more comfortable than the Philippe Professionel. When you look at your hand as you hold the bars, your palm forms a cup-shape. Well-designed Randonneur handlebars curve upward to fit into that shape perfectly. When we rode PBP on a tandem with these bars in 2003, my hands were in great shape after 52 hours on the road, even though I held onto the bars pretty much the whole time. Here is a photo of the position “behind the hoods” with the Grand Bois Randonneur bars:
The tops are not horizontal, but slope up from the stem, making the hand position on the tops (next to the stem) a little less comfortable. It’s a compromise: If you ride a lot behind the hoods, choose the Randonneur bars. If you climb a lot on the tops, the Professionel (or its modern incarnation, the Grand Bois Maes) may be better. I use both positions, yet I prefer the Randonneur.
In the 1920s, even racers used this handlebar shape. By the 1940s, it was specific enough to long-distance cyclists that it was called “Randonneur.” When you look at the best bikes in Paris-Brest-Paris, at touring bikes equipped for long trips, or at tandems of that era, you usually see them equipped with the AVA Randonneur handlebars.
The Randonneur handlebar shape is very subtle, and it’s important to get it just right. Nitto’s Randonneur handlebars copy the general shape, but they do not support the hands well. In fact, I find the Nitto’s model (slightly) less comfortable than standard bars. The Grand Bois Randonneur handlebar is based on careful measurements of the AVA, and Grand Bois went through a lot of effort to get the shape right.